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The effects of indolebutyric acid and irradiation on tomato fruit set and yield Taper, Charles Daniel 1948

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te 3  Co  THE EFFECTS OF INDOLEBUTYRIC ACID AND IRRADIATION ON TOMATO FRUIT SET AND YIELD  by Charles Daniel Taper  A Thesis Based Upon an Experiment Done i n the DEPARTMENT OF HOBTICULTURE and Submitted f o r the Degree of MASTER OF SCIENCE IN AGRICULTURE i n the FACULTY OF AGRICULTURE  THE UNIVERSITY OF BRITISH COLUMBIA  fO.  3?  /  THE EFFECTS OF INDOLEBUTYRIC ACID AND IRRADIATION OF TOMATO FRUIT SET AND YIELD ABSTRACT During the winters of 194-6 to 194-7 and 1947 to 1948 one hundred and twenty-eight tomato plants of the varieties Vetomold 121 and A i l s a Craig, growing i n a greenhouse at the University of B r i t i s h Columbia, were subjected to irradiation from 200 watt fluorescent lamps, and treated with organic acids, applied to f o l i a r and f l o r a l parts, i n an attempt to increase f r u i t set and yield. The plants were grown i n s o i l i n 10 inch pots placed i n randomized positions.  During the f i r s t winter they were treated i n  groups of eight; and, during the second, i n groups of six.  Control  groups were maintained. Sixty-seven days of irradiation from 200 watt fluorescent lamps, used to increase the normal photoperiod by six hours, produced, i n Vetomold 121, prounced damage to foliage and an inhibition of flowering. Pre-irradiation of seedlings of Vetomold 121 for four hours daily, following the greening of the cotyledons, resulted i n a significant increase i n set of 29.6 per cent for f i r s t clusters. A combination of this treatment and a water spray, on flov/ers, of indolebutyric acid,  5000  p.p.m., was, for f i r s t clusters, significantly  the most effective treatment applied to the variety. The i n i t i a t i o n of flowering i n tomatoes, i t was found, i s  2  governed by the length of the photoperiod; and i s not  influenced  by food relationships within the plant. Foliar sprays of indolebutyric acid 50, 100, 250 and 500 p.p.m., applied to Vetomold 121, prior to flowering, had no effect. Indolebutyric acid 100 p.p.m. and 200 p.p.m. i n water were ineffective i n influencing f r u i t set. "Fix", "Seed-Less-Set", and indolebutyric acid 5000, JGOO and 500 p.p.m., applied i n water, s i g n i f i c a n t l y improved f r u i t set 20.9 to 37.1 per cent on f i r s t clusters of the varieties. Hormodin No. 1, i n t a l c , used on the second clusters of Vetomold 121, increased set by 22.8 per cent.  No treatment was better than any other i n  influencing set, but indolebutyric acid produced f r u i t s of better shape than the commercial preparations "Fix" and "Seed-Less-Set". No treatment caused plant injury. Total yields were s i g n i f i c a n t l y increased by effective treatments; but average f r u i t si7.es were not increased. There was no difference due to variety, year, or time of planting. A delayed spray appeared to be the most convenient method of application; i . e . , one application made to each cluster when most of the flowers are open, with e a r l i e r flowers on the point of dropping. Parthenocarpic. f r u i t s were sweeter than seeded f r u i t s . Applications of effective concentrations of indolebutyric acid resulted i n the production of bands of uniformly sized f r u i t s  3  >  maturing at nearly the same time. Fruits from flowers treated with acid ripened five to seven days earlier than fruits developed from untreated flowers.  1  Where acid treatments were effective the formation of abscission layers was retarded and, as a result, there was no fruit drop. Of the materials and concentrations tested, indolebutyric acid 500 p.p.m. in water, applied as a delayed spray to floral parts, appeared to be the most valuable.  ACKNOWLEDGMENTS  The writer expresses h i s sincere and grateful appreciation to Dr. G. Howell Harris, Professor i n the Department of Horticulture, under whose direction the work was carried out^ f o r h i s suggestions and helpful criticisms during the entire period of the investigation; and to Dr. A. F. Barss, Professor and Head of the Department of Horticulture, for his kindly interest throughout the experiment.  FOEEWAKD  The following i n v e s t i g a t i o n was  conducted under the  d i r e c t i o n of the Plant N u t r i t i o n Section of the Department of H o r t i c u l t u r e of the U n i v e r s i t y of B r i t i s h Columbia during the sessions 1946  to 1947,  and  1947 to  1948.  The object of the experiment was to determine the e f f e c t s of i r r a d i a t i o n and indolebutyric aoid on tomato f r u i t set and  yield.  This information, i t was hoped, would suggest a means of increasing the percentage of flowers  developing  into f r u i t s , - thus a i d i n g the growers of commercial crops of tomatoes i n greenhouses i n the Vancouver area of B r i t i s h Columbia.  It was  f e l t that any such information  would be of p a r t i c u l a r value during the winter months; f o r i t i s then that f r u i t set i s least s a t i s f a c t o r y .  TABLE OP CONTENTS Page INTRODUCTION  1  Statement of the Problem Purpose of the Present Experiment Work of the F i r s t Year Work of the Second Year J u s t i f i c a t i o n for. the Present Experiment Relation to the Broad F i e l d I n t r i n s i c and P r a c t i c a l Value HISTORICAL DATA  1 1  PHYSIOLOGICAL FACTORS BASIC TO THE PROBLEM  27  DISCUSSION OF A RELEVANT EXPERIMENT  43  MATERIALS AND METHODS  48  PRESENTATION OF RESULTS  64  Tables DISCUSSION OP RESULTS  78  Analyses of Variance SUMMARY  88  CONCLUSIONS  92  BIBLIOGRAPHY  95  ILLUSTRATIONS Plates Faciig Page Fruits from Treated and Untreated Tomato Flower Clusters  72  THE EFFECTS OF INDOLEBUTYRIC ACID AND IRRADIATION ON TOMATO FRUIT SET AND YIELD  INTRODUCTION statement of the Problem In the northern United States, and i n Canada, one of the problems connected with the production of greenhouse tomatoes, during the winter, i s the low percentage of f r u i t get. Possibly this i s the major d i f f i c u l t y encountered. I t has been found that the tomato, unlike many plants, enters the flowering stage of the reproductive phase under conditions varying widely from the' optimum; but, although pollen i s formed, many flowers do not develop into f r u i t s ; the reproductive phase not continuing to completion.  This  low set appears to be due, more than to any other single cause, to a too brief photoperiod during the short winter days. It i s interesting to note, however, i n connection with photoperiodism and radiation, that tomatoes can be injured, and f i n a l l y k i l l e d , i n any day-length over 1 9 hours ( 1 ) . General Explanation of the Purpose of the Present Experiment The main purpose of the investigation reported here, stated b r i e f l y , was an attempt to discover a satisfactory method of inducing the setting of f r u i t s i n greater quantities than f r u i t set as a result of self-pollination i n the tomato varieties Vetomold 1 2 1 ,  and A i l s a Craig, grown experimentally, during winter months, under greenhouse conditions, and daylight conditions, as they display themselves i n the Vancouver area of B r i t i s h Columbia. The chemical}'-(indole-3)-n-butyric acid and two commercial preparations known as "Fix", and "Seed-Less-Set" were applied to foliage and flowers of the Vetomold 121 and A i l s a Craig varieties of tomato to see i f the desired result could be obtained.  In addition,  plants of the Vetomold 121 variety, not treated with a chemical growth regulator, had their day length increased by a r t i f i c i a l lighting.  Fruit set i n these plants was compared with that i n the  chemically treated plants;  and set i n both was compared with set i n  untreated control plants, growing i n normal daylight. Work of the F i r s t Year During the winter of 194-6 an experiment, terminated A p r i l 1947, was conducted, at the University of B r i t i s h Columbia, with the purpose of increasing f r u i t set i n the greenhouse grown variety of tomato Vetomold 121.  The attainment of the object i n view was  attempted i n two ways: {1) By. increasing the natural day-length through the use of a 200 watt fluorescent lamp; and by simulating this increase. (2) By applying indolebutyric acid i n varying concentrations i n water sprays and talc dust to ovaries and flowers. A study of experiments, covering the period from 1928  on,  seemed to indicate that certain naphthoxy compounds were often more effective i n increasing f r u i t set, and i n inducing the formation of  . parthenocarpic- f r u i t s , than was indolebutyric acid.  Naphthoxy and  phenoxy compounds showed more a c t i v i t y i n e f f e c t i n g growth responses; but the responses were often undesirable.  F o l i a r damage, and puffy,  hollow parthenocarpic f r u i t s , due to a too great stimulation, and a too rapid growth i n p e r i c a r p a l t i s s u e s of the ovary, were common. Indolebutyric acid, on the contrary, when applied i n concentrations of s u f f i c i e n t strength, proved a mild, but e f f e c t i v e , greenhouse growth regulator when used to induce parthenocarpic  fruiting.  Thus, i t was decided, i n attempting to adapt the hormone treatment of plant reproductive parts to our l o c a l Vancouver conditions, to use the organic chemical indolebutyrio acid. I r r a d i a t i o n of seedlings i n the f l a t stage f o r four hours d a i l y , f o r twenty-two days, resulted i n an increase i n f r u i t set on f i r s t c l u s t e r s only.  This was further increased by an additional  treatment of indolebutyric a c i d .  The t o t a l increase due to  p r e i r r a d i a t i o n alone was not as large as that effected by the growth regulator used alone; so that, p r a c t i c a l l y , there was small advantage i n seedling i r r a d i a t i o n unless accompanied by an acid treatment. Seedlings i n a subgrouping were subjected to a simulated long day; i . e , , a long dark period was broken into two shorter periods by means of a r t i f i c i a l i l l u m i n a t i o n . The response was as though the day had been long.  The breaking of the dark period  into shorter u n i t s achieved the same effect as a longer, and continuous  application of light.  A reversal of response appeared to  be caused i n a chain of reactions occurring i n the dark period.  - 4 This points to a f i n a n c i a l saving when lamps are used to a l t e r normal day lengths i n greenhouses. Another group of plants, given s i x hours d a i l y i r r a d i a t i o n , under the fluorescent lamp, at f i r s t developed, flowers which proved vegetative, and then ceased flowering. i r r a d i a t i o n , did they show f r u i t set.  At no time, while undergoing Ultimately, the e n t i r e f o l i a r  system of these plants turned yellow, withered, and displayed a large degree of physiological damage.  This, probably, was due to the  q u a l i t y of the a r t i f i c i a l l i g h t used.  Uponbeing removed to a normal  daylight area, new growth, both basal and terminal, a r i s i n g from these plants, showed normal health. A spray of water and indolebutyric acid, 5000 p.p.m. applied to flowers, and Hormodin Ho. 1 powder, a commercial preparation of indolebutyric acid, applied to ovaries of flowers whose stamens had been removed, s i g n i f i c a n t l y increased f r u i t set.  One was not  superior to the other i n e f f e c t i n g increased f r u i t set; but spray 5000 p.p.m. was more convenient of a p p l i c a t i o n . This l a t t e r concentration, i n a few instances, seemed to cause temporary epinasty from which there was a rapid and complete recovery.  A concentration  of indolebutyric acid 100 p.p.m. was completely i n e f f e c t i v e i n influencing f r u i t set i n the v a r i e t y . Ten and one-half hours appeared to be the lower l i m i t of the photoperiodic range necessary to induce flowering i n Vetomold 1 2 1 . The majority of plants flowered on reaching the length of day of t e n hours and twenty-nine minutes; but none flowered where the day was shorter than t h i s .  Work of the Second Year The sttempt, rna,de during 1946 to 1947, to apply, to l o c a l greenhouse conditions, the present knowledge of organic acids, as Inducers of increased f r u i t set i n winter tomatoes, having shown indolebutyric acid as being e f f e c t i v e when applied as a flower spray, but not having indicated the best concentration, the decision was made to conduct a continuation of the winter greenhouse experiment. The use of methods f o r applying hormones other than i n sprays was not considered; the inconveniences involved being too great, and any resultant advantages not being important enough to warrant t h e i r use. ::Pre-irradiation tests included i n the f i r s t part of the experiment were not again repeated, t h e i r e f f e c t s having been well demonstrated  the f i r s t year.  Other  l i g h t treatments were  f e l t to be worthy of investigation on t h e i r own accounts; so they were not attempted during 1947 to 1948. A study of the current l i t e r a t u r e on the topic of growth regulators seemed to uphold the wisdom of having determined upon the use of indolebutyric a c i d f o r the f i r s t year.  Therefore,  i t was decided to use i t again. The f i r s t year of the experiment having indicated a suitable material, i t was hoped that the second year would determine thenmost  -  6  -  effective concentration or concentrations. During the second year two varieties of greenhouse tomatoes, were grown, Vetomold 121 and A i l s a Craig, and some observations were made with regard to yields.  I t was f e l t that the second half of  the work would he more valuable i f i t dealt with fewer aspects of the problem under investigation.  Notwithstanding, the effects of  the two factors, variety and season were studied; though the main purpose was to determine the concentration of indolebutyric acid most suitable for increasing tomato f r u i t set on the f i r s t blossom clusters. J u s t i f i c a t i o n for the Present Experiment The "immense value of discovering some e f f i c i e n t , certain, and economical method of increasing f r u i t set i n greenhouse tomatoes, during the winter months, i s a matter of obvious import. In the Vancouver area of B r i t i s h Columbia the problem seems to be of particular moment. On an average,the annual r a i n f a l l of t h i s d i s t r i c t i s 57 inches per annum. By far the greater amount of this precepitation comes during the winter months; and the attendant number of hours of cloud, fog, and overcast i s proportionately great. These may be adverse conditions i n that they may lower the v i a b i l i t y and stimulating qualities of pollen, or inactivate i t by increasing i t s moisture content;  but i t i s doubtful i f light intensity i s enough  reduced to prevent a sufficient production of carbohydrates for growth, f r u i t i n g and maturation; though we know, that to get f r u i t i n g , after an i n i t i a l l y rapid vegetative growth, there should be, along with # See  pp.-  71.  - 7 ample nitrogen and water, an excess of carbohydrates over and above the amounts u t i l i z e d with the nitrogen  (2).  A l i c e P. Withrow says: "This low set i s due to f a u l t y p o l l i n a t i o n caused i n turn by the low carbohydrate content of the plant occurring during the cloudy, short days of our northern winter. Freeman S. Howlett (4), who  I t i s l o g i c a l . ."(3')  i s an authority on the subject,  i s c i t e d as support f o r t h i s statement; but i t would appear that the assumption may be due to a misinterpretation of Howlett,  who,  perhaps, was r e f e r r i n g to d e f i c i e n c i e s r e s u l t i n g from other causes. One must bear i n mind that noon daylight, during the summer, can be reduced to one-twelfth i t s value before any decrease i n the rate of photosynthesis occurs ( l a ) .  O r d i n a r i l y , there Is much more l i g h t  available i n nature than plants can absorb i n photosynthesis, so long as other factors, such as carbon dioxide supply, remain the same. In t h i s region, n u t r i t i o n a l "..abnormality has not been noted i n winter growth; and i t would appear that, at f r u i t i n g time, there i s , where c u l t u r a l practices have been normal, an excess of carbohydrates s u f f i c i e n t to provide f o r the production of f r u i t buds and of f r u i t . I t i s a matter of stimulating the plant to u t i l i z e materials present within i t .  This being so, there appears to be no n u t r i t i o n a l reason  why p o l l e n or p o l l i n a t i o n should be faulty; though possibly p o l l e n v i a b i l i t y may be impaired under poor l i g h t conditions. Possibly the minimum photoperiod necessary to flowering may not s u f f i c e to produce p o l l e n containing those stimulating substances necessary to  -  fertilization;  8  -  the r e s u l t being poor set i n midwinter.  I t may  be  that periods of lowered l i g h t i n t e n s i t y , during which i t i s possible that l i g h t q u a l i t y may be varied, may have some diminishing e f f e c t on that amount of f r u i t set which may daring short days. may  normally be predicted even  I t i s possible, too, that c e r t a i n kinds of glass  vary l i g h t q u a l i t y adversly.  Whether there are such factors or not,  i t s t i l l remains that winter i s a short*'day period of the year; and a r t i f i c i a l l y increasing day-length, then, would seem a l o g i c a l undertaking from which only b e n e f i c i a l effects should r e s u l t . I f s u f f i c i e n t photosynthesis  takes place i n winter to provide  f o r the production of f r u i t , i t seems not unreasonable to hope that, other than an optimum photoperiod, some s a t i s f a c t o r y means of stimulating f r u i t set may be found.  Tomatoes do flower during short-*  day seasons of the year, even though f r u i t set i s poor.  Thus, the  reproductive phase, the period of f i n a l maturation, does commence, though i t may  not be c a r r i e d to  a s a t i s f a c t o r y conclusion.  This  knowledge provides one with a s t a r t i n g point; and the concept of a chemical stimulus, applied to the flower, r e a d i l y suggests i t s e l f . I t i s , perhaps, possible that a hormone spray may  induce  f r u i t s e t t i n g i f applied to the roots or f o l i a g e , of a plant to flowering. cuttings (5); epinasty.  previous  This method has been used to stimulate rooting i n but treated f o l i a g e frequently displayed a marked  F r u i t spurs on apple trees have been treated to influence  the i n i t i a t i o n of f r u i t buds (6).  Thus a further method of approach  to the problem of f r u i t set i n the tomato i s suggested; a way which  _ 9 may  warrant a thorough, separate i n v e s t i g a t i o n at some future time. Local temperature conditions are very favorable to greenhouse  Operation;  the amount of f u e l required to maintain proper heat being  about one t h i r d that required at Winnipeg, thus making operating costs measurably lower.  I f problems, such as t h i s p a r t i c u l a r one  of f r u i t set, can be overcome, conditions, i n general, warrant an expansion of the industry, which, on the whole, i s a very p r o f i t a b l e one, and i s i n a generally healthy economic state.  I f the greatest  d i f f i c u l t y for tomato growers, that of unsatisfactory winter f r u i t set, can be s a t i s f a c t o r i l y solved, the greenhouse industry might benefit, very l a r g e l y , i n a f i n a n c i a l  way.  Relation to the Broad F i e l d The present experiment i s related, generally, to work being done i n f r u i t set. may,  In the future, other chemicals and means  possibly, be used to induce f r u i t s e t t i n g i n tomatoes.  be asked i f the problem a f f e c t s other crops. gained here may be of more extensive value.  I f so, any  information  More l i g h t may be  thrown upon the subject of parthenocarpy i n plants. question of parthenogenesis may be touched.  I t may  -  The f a s c i n a t i n g  More broadly, there i s  yet much to be learned regarding n u t r i t i o n ; the u t i l i z a t i o n of nutrients i n the f u l l development to maturity of a plant; and such factors as r a d i a t i o n , day length, plant hormones, and a l l elements which exert an influence on such u t i l i z a t i o n .  I t i s here that t h i s  one problem enters the whole, wide f i e l d of plant  physiology.  10 -  I n t r i n s i c and P r a c t i c a l Value A j u s t i f i c a t i o n f o r performing the present experiment has already "been developed; "but, to be of b e n e f i t to the greenhouse industry, the discovery of a good method of increasing f r u i t set i n greenhouse tomato plants during the winter, i s not, i n i t s e l f , enough.  An increase i n the number of f r u i t s set, and i n the t o t a l ,  quantity of such f r u i t s , must be great enough to warrant the use. of the method producing them; i . e . , the method and equipment, should be inexpensive and economical of time and labour.  Chemicals  should  be r e a d i l y obtainable at low cost; and they should be capable of being e a s i l y and quickly applied by means of simple  apparatus.  HISTORICAL DATA The f r u i t of the tomato i s recognized, as being one of the more n u t r i t i o u s and valuable foods; p a r t i c u l a r l y because of i t s high vitamin C content.  Hence, i t can r e a d i l y be seen that i t would not  only be a boon to the populace at large, but, i n a more r e s t r i c t e d sense, an important  a i d to the commercial operation of greenhouses  i f t h i s problem of set could be attacked and solved i n an e f f i c i e n t and economical way.  Since the year 19?6 many experiments have been  conducted i n attempts to overcome the d i f f i c u l t y . The tomato, though o r i g i n a l l y a short-day plant, has been developed into one p r e f e r r i n g a long. day.  Therefore, an increase  over winter day-length should b r i n g the plant nearer to pptinrnm conditions.  For t h i s reason, one of the f i r s t ways which suggests  i t s e l f , when one ponders a s o l u t i o n to the problem of set i n the tomato, i s that of attempting to increase the length of day by means of a r t i f i c i a l l i g h t i n g during winter months.  This has been  done i n many commercial greenhouses as a routine p r a c t i c e .  Forty  watt internal r e f l e c t o r lamps,- and l i g h t s of even lower i n t e n s i t y , appear to have given r e s u l t s which, though not s c i e n t i f i c a l l y recorded and analyzed, have warranted costs.  Experimenters have used lamps  of much greater i n t e n s i t y (3)# Since the discovery of the relationships between plants and various organic acids, plant hormones, and plant vitamins i n the r o l e of growth regulators, promoters and accelerators, another method of approaching the problem of set has led to a great number of  new  - 12 experiments being done.  These various substances were f i r s t used  to promote rooting i n woody cuttings from plants d i f f i c u l t to propogate vegetatively.  Later, an attempt was made to improve  results by spraying the plants before removing the cuttings (5). F i n a l l y , an e f f o r t was made to increas.e growth i n plants, p a r t i c u l a r l y i n the size of f r u i t , by spraying, or dusting the accelerating substances as a step i n a c u l t u r a l method.  Results obtained from  these experiments, together with r e s u l t s obtained from experiments i n stimulating parthenogenesis  i n animal organisms (7), seemed to  indicate that chemical stimulation might lead to the production of f r u i t s i n plants when no f e r t i l i s a t i o n had taken place.  Since  then, a great many attempts have been made to induce the setting of parthenocarpic f r u i t s i n tomato plants by spraying the flowers with growth regulators.  Some substances have been shown to have a  retarding effect on growth i n general (8).  Some have been shown to  cause i n j u r y under c e r t a i n conditions, or i n p a r t i c u l a r concentrations. With other chemicals, c e r t a i n experimenters have obtained no r e s u l t s ; while, with the same chemicals, others have been c o n s i s t e n t l y successful i n obtaining increased set of f r u i t , and larger, though seedless f r u i t s , or a larger quantity  of good q u a l i t y , smaller f r u i t s .  Perhaps the foremost amongst these l a t t e r investigators i s Freeman S. Howlett, of the 0Mo Ohio.  A g r i c u l t u r a l Experimental  Station, Wooster,  However, despite a l l the attempts to solve the problem of  set i n the tomato plant, r e s u l t s have not always proven conclusive.  i  Hot u n t i l t h i s year, 194-8, has the work progressed much "beyond the experimental stage.  I t appears that, even now,  some p r o f i t a b l e work  could s t i l l be done i n determining the results from treatment i n d i f f e r e n t months and at different periods of growth, To date, indolebutyric acid has shown the most consistently good r e s u l t s i n inducing the production of parthenocarpic f r u i t s on tomato plants.  Other substances, such as indoleacetic acid,  naphthaleneacetic acid, and indolepropionic acid have given f a i r l y good r e s u l t s .  Beta fiaphthoxyacetic acid i s very e f f e c t i v e ; but  damaging to plant t i s s u e s . There are, now,  These compounds have been expensive.  the l e s s - c o s t l y , halogenated phenoxy acids.  Some  of these have been found to improve tomato f r u i t set when the acid i s applied to flowers i n relatively!'low concentrations.  One,  2-4 dichlorophenoxy propionic acid has been used quite successfully. Others, which may be suggested, are 2-4-5 trichlorophenoxyacetic acid, i t s sodium s a l t , sodium trichlorophenoxyacetate, and 4 chlorophehoxy acetic a c i d .  Two-4 dichlorophenoxy a c i d must be used  i n extremely d i l u t e concentrations, because i t i s known to cause injury.  Orthochlorophenoxyacetic acid i s e f f e c t i v e , but there are  indications that outer tissues may develop at a more -'rapid rate than placental tissues, the result being a hollow, collapsed f r u i t . Many growth regulators produce similar effects when used i n high concentrations.  In such cases the f r u i t s often f e e l puffy, or  spongy to the touch. These organic acids have been sprayed or applied to flowers i n varying concentrations. Carriers used have been ethyl alcohol or  - 14 carbowax.  These have been dissolved i n water to make sprays; or  mixed with l a n o l i n paste, or t a l c dust, to make preparations .suitable f o r dry applications. "Prepared i n the l a t t e r way, hormones are somewhat d i f f i c u l t of application to flowers. The conception of animal hormones was accepted as long ago as 1914; and as early as 1927 i t was known that some substance, or substances, within plants, could stimulate growth (9).  In 1928,  Went, of Holland, i s o l a t e d plant hormones; but, i n general, these growth substances were completely unknown. more knowledge of t h e i r nature.  Experiments soon provided  I t was learned that they could  influence plant growth i f applied to the outer surfaces of stems, roots or f o l i a g e .  The Sitka g a l l midget does t h i s very thing i n  nature, manufacturing a hormone, similar, chemically, to those produced within a plant, and applying t h i s powerful substance to twig ends, inducing an extreme growth resembling a pine cone, green i n colour. In 1929 a long paper on the subject of hormones was published by a German s c i e n t i s t , Arthur Pesek (10). By 19?6, F e l i x Gr. Gustafson, an American, had induced the production of seedless tomato f r u i t s by the a p p l i c a t i o n , to the stigma and cut' surface of the styles of mature.flowers, i n l a n o l i n pastes.  of various substances  One material used was indolebutyric acid.  In  concentrations of 0-.J per cent the l a t t e r was found to be somewhat more e f f e c t i v e than any other chemical used ( 1 1 ) ,  By 1938 the hormones auxin a and auxin b were well known. Beta-indolyl-acetic acid had "been discovered to have growth stimulating properties similar to those of the auxins, and was heteroauxin.  called  This substance was discussed i n many s c i e n t i f i c papers  of the period.  H. Herbst, of Germany, published a paper, i n 193*9,  which showed that i n greenhouses, or i n locations where p o l l e n cannot be t r a n s f e r r e d by a i r currents, the application of heteroauxin to tomato flowers induced the production of small, parthenocarpic fruits.  He found that Beta-indolyl-acetic acid 0.1 per cent, i n  water solution, on foliage and f r u i t of the tomato, increased the y i e l d 5 to 2 0 per cent by weight, but made the f r u i t spotted and unm aufe jab l e !  (12).  In 1939, Gustafson found that, i n the John Baer v a r i e t y of tomato, f r u i t s e t t i n g as a r e s u l t of the chemical treatment flowers, was as great as by p o l l i n a t i o n .  of the  Parthenocarpic f r u i t s  were smaller than seeded f r u i t s , except where the s o i l was  very  r i c h (11a). Freeman S. Howlett, i n the United States, has , probably, undertaken the greatest number of experiments concerning the p r a c t i c a b i l i t y of chemical applications to flowers i n inducing increased f r u i t set i n the tomato plant.  In an experiment concerning  the p r a c t i c a b i l i t y of c e r t a i n chemicals as a means of inducing f r u i t set i n the tomato plant, 1939 to 1940, he found that indolebutyric acid was more e f f e c t i v e than indoleacetic acid^\  at  concentrations 0 . 5 , 0.1 and 0.02 per cent, i n l a n o l i n paste, i n  -  16 -  causing the development of flowers into f r u i t and i n producing larger f r u i t s ( 1 3 ) .  With the v a r i e t i e s Globe and Marhew, indolebutyric  was best at p.»5 p e r c e n t and poorest at 0.02 per cent. r  K indoleacetic  and K naphthalenacetate gave f a i r l y good e f f e c t s at 0 . 0 5 per cent, concentrations.  Fruits induced by indolebutyric acid tended to be  larger than those produced following s e l f - p o l l i n a t i o n . were well f i l l e d .  Locules  Quality was as good as f r u i t produced naturally.  The l o c a t i o n of the experiment described above was not mentioned i n the reference, but i t was probably at the Wooster, Ohio A g r i c u l t u r a l Experimental s t a t i o n . In $914:1, Howlett, at the Ohio A g r i c u l t u r a l Experimental Station, deprived tomato flowers of pollen, and induced f r u i t set by means of 0 . 3 per cent indolebutyric acid i n l a n o l i n paste.  He  concluded that indolebutyric a c i d l e f t l i t t l e to be desired i n achieving h i s purpose 0 3 a ) . In 1942, Howlett found indolebutyric acid to give i t s best r e s u l t s with the e a r l i e r flower clusters f o r , as day-length increased, natural set became correspondingly greater ( 1 3 b ) . his  experiments  In 1945, he repeated  , using the same acid i n a spray ( 1 3 c ) .  T. Swarbricke, Long Ashton Eesearch Station, 1942, found O.OJi per cent solutions of naphthaleneacetic acid, and naphthoxyacetic acid on tomato plants resulted i n a check to t h e i r development, and i n marked epinasty on the parts touched (14). T. W. Brets found v o l a t o l i z e d growth promoting  substances  caused d i s t o r t i o n of tomato plants and f r u i t s grown i n greenhouses (15).  - 17 A successful experimenter with acids i s P. W. Zimmerman of the Boyce Thompson I n s t i t u t e for Plant Research, Yonkers, Hew  York (16).  In a professional paper, "Substances E f f e c t i v e f o r increasing F r u i t Set and inducing Seedless Tomatoes", published i n the "Proceedings of the American Society for H o r t i c u l t u r a l Science", i n 1944,  P.  W.  Zimmerman, and A. E. Hitchcock gave a report on some of the work done up to the year 1944,  a  t the Boyce Thompson I n s t i t u t e Laboratories, to  locate e f f e c t i v e chemicals f o r inducing parthenocarpy.  The paper i s ,  also, an admirable summarization of the greater part of a l l s i m i l a r experiments previously completed. These men  found that Beta naphthoxyacetic acid, and some of  the substituted phenoxy and benzoic acids may  have pronounced  formative influences on a l l plant tissues, causing injury, epinasty, and modification of habit.  A plant's general condition i s a f a c t o r  which leads to r e s u l t s varying with each experiment, so that the choice of these materials f o r inducing parthenocarpy i s , at best, doubtful.  They r e f e r to such substances as being a c t i v e .  Indolebutyric  a c i d they found to be a mild and inactive regulator. They found, from a concentration standpoint, that the most e f f e c t i v e chemical known for stimulating ovary growth was 2,  4-dichlorophenoxyacetic  acid, but, that, unfortunately i t was the  one  most l i k e l y to cause i n h i b i t i o n of growth and modification of leaves. Above 5 mg/1  i t affected areas of the plant other than flower parts.  They thought 5 mg/1, the ovary.  however, nearly optimum f o r stimulating growth of  I t would^ therefore, appear that i t can, i n some cases, be  -  used safely.  18  -  With a vigorous grower; such as Vetomold, unduly sensitive,  "because of i t s succulence, to any chemical treatment, the use of t h i s acid may be ruled out as e n t a i l i n g a too great r i s k . These experimenters found the percentage of f r u i t set on treated plants to be from one to 19 per cent greater than that on p o l l i n a t e d , but untreated, controls.  The q u a l i t y of parthenocarpic  f r u i t depended to some degree upon the s e n s i t i v i t y of a variety to growth substances.  The persistence of f l o r a l parts was a c h a r a c t e r i s t i c  response on the part of treated plants.  E n t i r e l y seedless f r u i t  was d i f f i c u l t to procure where p o l l i n a t i o n occurred; but the more rapid development, and larger size of f r u i t s from treated flowers was evidence of a stimulative e f f e c t . Aerosol and vapour methods of dispensing growth promoters exposed the entire plant to chemical a c t i v i t y .  They thought compounds  active f o r parthenocarpy might be found which would not greatly i n h i b i t plant growth. important.  The aerosol method would then become more  An entire greenhouse of 10,000 cubic feet capacity might  be treated at one time; which would be a very  great  convenience  indeed. For inexperienced growers, and those working with only a few plants, Zimmerman and Hitchcock f e l t that water solutions, applied with an atomizer, were to be recommended, and that the spray should be applied to the back of the buds and the flowers, and to the open side of the flowers. Zimmerman found the physiological a c t i v i t y of hormones to be r e l a t e d to chemical structure (16a).  :A  - 19 A l i c e P. Withrow, Purdue U n i v e r s i t y A g r i c u l t u r a l Experimental  Station, Lafayette, Indiana, (2), compared f r u i t set  i n tomato plants,treated with a r t i f i c i a l irradiation^.w i t h set i n plants on which the flowers had "been treated with indolebutyric acid.  This experiment has a special significance for the present  investigation, and w i l l be r e f e r r e d to again. In 1944, A. Pollard, M. E. Kieser, and Joan Steedman reported that the food value of parthenocarpic tomatoes was as high as that of seeded f r u i t s .  Seedless f r u i t s were sweeter, and lower i n ascorbic  acid content, but not s i g n i f i c a n t l y so (17). In 1945 Howlett published a further report  (13d),  showing  that he had found Beta naphthoxy acetic acid, and 2-4-dichlorophenoxyacetfc acid to increase tomato size, but that the treatments resulted i n c a v i t i e s f i l l e d with an undesirable gelatinous pulp, and i n an abnormal growth of leaves.  He further reported that indolebutyric  acid had been adopted by commercial growers of greenhouse tomatoes i n Ohio, for the treatment  of spring crops.  A 0.2 per cent '  application i n water spray was r e s u l t i n g i n f r u i t sets of up to 90 per cent.from a l l flowers formed.  In view of the fact that  experiments i n the a p p l i c a t i o n of growth regulators to tomato flowers were widely conducted i n 1946 and 1947, one can but conclude that these growers were themselves experimenting, scale.  though on a large  The r e s u l t s reported were, apparently, not made from  accurately kept records.  Further, i n view of the fact that t h i s  a c i d was s e l l i n g to experimenters  at that time, i n the pure state ,  for as much as f i v e d o l l a r s a gram, t h i s information i s of great  I  - 20 interest indeed.  Unless the price of the material was greatly  reduced to commercial growers  which i s probable  the cost of  treatment would hardly have been warranted, even by the greatly increased crops. During the year 1946, M. C," Strong found one application of 2, 4-dichlorophenoxyacetic acid (2, 4-d) 10 p.p.m., when sprayed on flower clusters, to increase tomato size and decrease the time of bloom to maturity by one to two weeks.  Some parthenocarpic f r u i t s  were hollow; many of these being unmarketable (18). Also, i n 1946, F. S. Howlett and E. B. Withrow reported indolebutyric acid to be generally non-injurious when applied to the flowers of tomatoes.  Howlett stated that 2000 p.p.m. was  an e f f e c t i v e concentration, increasing f r u i t size.  Aqueous  solutions were e s p e c i a l l y good, and saved time, but f r u i t s so stimulated may show an increased s u s c e p t i b i l i t y to blossom end rot (13e and t 3 f ) . A more recent paper i s one supplied by H. K. Kemp, of A u s t r a l i a , i n 1 9 4 7 , He found Beta naphthoxyacetic acid,100 p.p.m., applied to tomato flowers, to increase growth without-fruit;, distortion.  The chemicals 2, 4-dichlorophenoxyacetic acid, \® p.p.m.,  and 2, 4, 6 trichlorophenoxyacetic acid, 50 p.p.m., induced parthenocarpy with distorted growth (19).  -21Some of the more recent l i t e r a t u r e dealing with growth regulators may he found i n the Yearbook of Agriculture, U. S. D. A., 1943-194-7, published i n 1947. John W. M i t c h e l l discusses growth regulators and greenhouse tomatoes.  He states that, because there  are few insects or a i r currents i n greenhouses i n winter, one must p o l l i n a t e tomato flowers by shaking;  but that hand p o l l i n a t e d flowers  often f a i l to set a high percentage of f r u i t , e s p e c i a l l y i n cloudy weather.  Often t h i s i s due to the f a i l u r e of the flower to  produce a pollen of a vigorous kind, similar to that developed by f i e l d plants i n the summer.  Vigorous pollen serves to f e r t i l i z e  so that seeds develop, and, also, apparently, contains substances which stimulate the development of the ovary into f r u i t .  The place  of these substances may be taken by growth regulators, a r t i f i c i a l l y applied.  Flowers should be sprayed, when f u l l y open, with a 0.2  per cent water solution, or emulsion, of indolebutyric acid.  This  i s the most widely used and safest means of attaining the desired result.  I f an emulsion i s used, i t should contain l a n o l i n 1 to 2  per cent.  I f e n t i r e l y seedless f r u i t i s desired, i t i s necessary  to cut o f f the stamens at the time of treatment.  The aerosol  bomb method o f application i s s t i l l i n the experimental stage. Indolebutyric acid i s a r e l a t i v e l y mild, greenhouse regulator.  Baphthoxyacetic acid holds some promise when mixed  with indolebutyric acid.  Most other active compounds, naphthoxy  and phenoxy, cause the pericarp of the f r u i t to grow f a s t e r than inner parts, leading to the formation of hollow f r u i t s .  - 22 — Sterile fruits often surpass others in size and quality. However, most fruits from treated flowers will show evidence of pollination by the development of seeds (20). Also in the U. S. D. A. Yearbook for 1947 is a discussion of day length and flowering by H. A. Borthwick (21). This topic, of course, also relates to the present investigation.  Borthwick  summarizes the latest information regarding photoperiodism. Borthwick states that Garner and Allard have found the photoperiod to have an effect on functions of the plant other than flowering. Thus, a plant may have several photoperiods, one for each function. For instance, a certain photoperiod may determine the time of flowering in the potato, while a different one will provide optimum light conditions for full tuber development. For any photoperiod there may be a difference in response from two different organs. It is obvious that, for field plantings, a variety should be chosen whose day-length requirements are satisfied by those prevailing in the locality i-n question. One-half hour of difference in day-length may be responsible for as many as fifteen days difference in the flowering date. Thus, rather small differences in day-length may have important results. The size of a plant and its general maturity do not determine the time of flowering. The lower limit of its flowering photoperiodic range does. A very young and small plant may flower i f i t is. subjected to its flowering photoperiod. However, the longer a plant has grown vegetatively, and the bigger and more vigorous i t is,  - 2} the more flowers and heavier y i e l d there w i l l he.  A short-day plant,  seeded i n A p r i l , w i l l not flower u n t i l the f a l l , when days commence to shorten.  Such a plant w i l l have had time to become large  through vegetative growth. Borthwick states, that J . E. Knott, of the U n i v e r s i t y of C a l i f o r n i a , found plants to receive the stimulus of photoperiod through the leaves.  He discovered t h i s by exposing the leaves of  spinach to long photoperiods, while the stem growing point and very young leaves i n the centre of the rosette received short photoperiods.  These plants produced seed stalks as did controls  r e c e i v i n g long days.  Others r e c e i v i n g long photoperiods  on  growing points, and short one on the leaves, remained vegetative, as did the short-day control plants. The effects of photoperiod may be expressed by parts:of plants not subjected to i t .  SometimesVflower production, as a  r e s u l t of a favourable photoperiod, remains l o c a l i z e d on the treated part, but not always.  Often, flower buds form on untreated parts  i f leaves are removed from them; f o r these leaves seem to i n t e r f e r e with the t r a n s l o c a t i o n of the flower-inducing stimulus from a treated to an untreated area. The stimulus, apparently, moves from leaves to growing points, the areas i n which hormones are most often found.  (It i s  to be noted that some investigators have thought that the stimulus originates i n growing points.)  There i s a strong i n d i c a t i o n that  a chemical growth regulator i s involved.  Short-day plants flower not "because the photoperiod but because of the long period of uninterrupted dark.  i s short;  I f the dark  period i s broken, say, into two short ones, by an a r t i f i c i a l  light  interruption of less even than one minute, the effect becomes that of a long-day and flowering i s retarded.  I f the dark period i s long,  one minute interruptions b r i n g long-day plants into flower.;  Reversal  of response i n each type seems to be caused by a break i n a chain of reactions occurring i n the dark period,  Hence the term  "photoperiodic e f f e c t " may be somewhat of a misnomer. The effect created i n the case of long-day plants, by b r i e f interruptions i n the dark period,is thus the same as that created by extending the photoperiod with a r t i f i c i a l l i g h t added to one end of thecday;  an ordinary greenhouse procedure.  A'saving i n  costs i s here indicated. A long period of l i g h t , followed by a long period of dark, w i l l not prevent a short-day plant from flowering.  Thus,  the long period of dark i s required, not the short period of l i g h t . Similarly, long-day plants w i l l flower with short periods of l i g h t i f the uninterrupted periods of dark are, also, short. A short day does not prevent flowering, a long night does. Photoperiods,  of course, have a photosynthetic  Light i n t e n s i t y must be such, during photoperiods, photosynthesis  function.  that active  w i l l take place.  The photoperiodic mechanism i s fundamentally the same f o r both long and short-day plants. during the dark period .  Responses depend upon reactions  The leaves of long-day plants grafted to  - 25 short-day plants may cause the latter to behave like long-day plants. The wave lengths of light required to inhibit'flowering of short-day plants, by the interruption of long periods of dark, are the same as those required to bring about flowering of long-day plants under similar conditions. It has been found that a flower-inhibiting substance is not produced in the leaves of short-day plants growing in long photoperiods { pp.279 ). It is merely that leaves of short-day plants fail to supply a flower-inducing substance* or enough of i t , i f the dark period is short, and not long.  Leaves of long-day  plants may fail to supply a flower-inducing substance when the dark period is long.  The reason for this is obscure.  There is no evidence as to the chemical nature of flower-inducing substances produced in a plant (pp.279). Apparently the quality of light is an important factor in photoperiodic effect. One leaf, i f subjected to a flowering photoperiod, gives, apparently, enough leaf surface to provide a stimulus. If the nature of the substance manufactured in the plant could be determined i t might be applied externally and photoperiod ignored, in so far.as the date of flowering is concerned. All these experiments, and those of a similar nature, typify the kind of work done to date. It is quite possible that obscure publications, particularly in Germany, may record earlier work. It is quite possible that, in the same country, as early  -  26  -  as 19?0, and perhaps e a r l i e r , experiments without publication of results may have been conducted i n attempts to induce parthenocarpic f r u i t i n g . here with such work.  However, one need not be concerned  - 27 PHYSIOLOGICAL FACTORS BASIC TO THE PROBLEM It may  not be out of place to give, here, a consideration to  some of the physiological conditions of growth i n plants. The actual foods of a plant are carbohydrates, f a t s , proteins, and the vitamins or accessory foods.  Out of carbon dioxide, water,  and a l i t t l e of various s a l t s , plants construct t h e i r own tissues. Under the anabolic phase of metabolism, we may  consider.the  synthesis  of carbohydrates (photosynthesis); the synthesis of f a t s and o i l s ,  and  proteins; and, f i n a l l y , the conversion of these foods into protoplasm ( a s s i m i l a t i o n ) . The catabolic phase i s digestion, r e s p i r a t i o n , and  fermentation  or anaerobic r e s p i r a t i o n , such as takes place i n seeds. The essential a c t i v i t y of a plant i s i n the top, where, i n green parts, chlorophyll absorbs energy f o r the a c t i v i t i e s of l i f e from ether waves forming c e r t a i n portions of the spectrum of v i s i b l e l i g h t , solar or a r t i f i c i a l .  A series of reactions takes place whereby  plants b u i l d carbohydrates from what are commonly thought of aas the products of combustion; i . e . , carbon dioxide from the a i r , and water obtained through the roots, from the s o i l .  Chlorophyll, and substances  i n the structure of the p l a s t i d s containing i t , are intermediarily essential i n the synthesis.  Chlorophyll, as well as absorbing  probably take a chemiczl part i n the process. catalysts, are the a c t i v a t o r s .  light,  Enzymes, organic  Chlorophyll i s continuously  by l i g h t ; but cannot be manufactured i n i t s absence.  destroyed  Carbon, hydrogen,  - 28 -  oxygen, and nitrogen, with magnesium, are constituents of the chlorophyll molecule.  Iron i s not; hut i t seems to he necessary  to chlorophyll formation; and i t perhaps stimulates r e s p i r a t i o n ( l a ) . W i l t s t a t t e r has shown magnesium to he the only metal constituent of chlorophyll.  Iron may he necessary to i t s u t i l i z a t i o n .  Carbon dioxide and water are found i n the flues of furnaces and i n the r s p i r e d breaths of animals.  Being products of combustion,  they cannot provide the primary energy used -in b u i l d i n g foods.  5Che  energy, that i s used, i s the same energy that i s required to activate the receiving apparatus of a radio set.  Thus, plants are a form  of solar engine. In most plants, the f i r s t stable product of photosynthesis i s the soluble sugar glucose.  Oxygen i s a by-product.  Usually the  sugar - i s immediately changed to starch i n the l e a f , f o r starch i s insoluble i n water, and does not obstruct the osmotic properties of c e l l s ; neither does i t retard the photosynthetic processes through the accumulation Of end products.  At night the starch  i s converted back to sugar, and i s removed from the leaf, through the veins, to other parts Of the plant. free of starch i n the  Leaf c e l l s are thus  morning, and can hegin photosynthesis again,  and continue the process of storing l i g h t energy i n the foods manufactured; the energy being stored i n the form of insoluble polysaccharides; i . e . , ustarch, glycogen, i n u l i n , c e l l u l o s e , hemicelluloses. A l l interactions occurring within the plant, following photosynthesis, are activated by enzymes.  Hence, temperature i s an  -  29 -  important factor i n plant function. slowed by lowered temperatures.  The a c t i v i t y of enzymes i s  The average production of  carbohydrates, i n many common plants, i s somewhere i n the neighborhood  of 1g. per square meter of leaf surface per hour { l b ) .  Carbohydrates, formed by photosynthesis, serve not only as sources of carbon, hydrogen and oxygen to combine wi^h nitrogen, and smaller amounts of other materials, i n the synthesis of proteins, but as the plant's sources of energy released during r e s p i r a t i o n .  "Starch, c e l l u l o s e , and other carbohydrates are made d i r e c t l y out o f the o r i g i n a l glucose r e s u l t i n g from photosynthesis. Some of the glucose i s converted into g l y c e r i n and f a t t y acids from which f a t s are made. By the addition to glucose of such minerals as n i t r a t e s , phosphates, and sulphates, amino acids are made.  These,:Lin turn, are linked together to  form proteins, always found i n abundance where there i s a c t i v e c e l l d i v i s i o n and growth.  Out of the proteins may be  made enzymes, secretions, other complex organic compounds, and protoplasm i t s e l f .  The making of the l i v i n g  protoplasm i s c a l l e d a s s i m i l a t i o n .  substance  Assimilation i s the  • lultiineftelgoal' of alFaandboJlocprQeesseB.  It i s really  i n a s s i m i l a t i o n that the nonliving substances become l i v i n g " . ( 1 c ) .  Because of protoplasm a plant i s capable of self-reproduction which, i n a f i n a l a n a l y s i s , i s a process of flowering, f r u i t  setting  - 30 and f r u i t i n g , which i s maturation. Secondary reactions, the oxidation of the products o f synthesis Into protoplasm, take place i n the dark.  In t h i s secondary a c t i v i t y  the plant works l i k e a heat engine, by oxidation of the substances 1  synthesized by sunlight.  Oxygen r e s p i r a t i o n involves the u t i l i z a t i o n  of free oxygen, at l e a s t i n the f i n a l stages of the process, and r e s u l t s i n complete oxidation to carbon dioxide and water.  The  r e a l l y important feature i s that energy i s released by i t . Most of the energy l i b e r a t e d does not appear as heat; but i s used i n carrying on the work of the c e l l s .  Synthesized substances  are used as f u e l i n an engine, and release the usual products of combustion, oarbon dioxide and water.  In the dark, the plant works  more l i k e an animal, l i v i n g on substances made by a p l a n t — i n t h i s case i t s e l f — d u r i n g sunshine hours. dark —  Most growth takes place i n the  ten times as much as i n daylight.  Growth s i g n i f i e s hydrolysis,  digestion, and starch back to sugar. Soluble nitrogen i s most abundant i n the dark;  and proteins are thus most abundant where there i s active  growth and c e l l d i v i s i o n . Respiration i s oxidation of digested foods.  I t i s a process  to which l i g h t i s not necessary, though l i g h t stinulates i t , by providing respirable material.  indirectly,  Digestion, or hydrolysis of foods  into soluble substances, which supply growth, may, also, be said to supply the energy f o r growth (22); sugars.  In the process there i s a loss of  Carbohydrates are e a s i l y digested, and are, therefore, used  most i n r e s p i r a t i o n .  They are the most available source of stored up  -  31  -  radiant energy; and are a sort of storage battery ready to break down and combine with oxygen to release energy i n a form protoplasm can employ. Cytochrome, a substance common to a l l l i v i n g c e l l s , appears to have a fundamental part i n the u t i l i z a t i o n of oxygen by protoplasm, and has s i m i l a r i t i e s with chlorophyll. It has long been claimed that the requirements of a plant are not f o r l i g h t , but f o r the products of l i g h t .  With regard to a  plant's obvious needs f o r carbohydrates, t h i s i s very apparent. may  It  seem, a f t e r reading through the present work, e s p e c i a l l y those  portions emphasizing optimum photoperiod requirements, that an attempt has been made to reverse t h i s statement. w i l l show that t h i s i s not the case.  A little  thought  I f a certain^,photoperiod i s  required to b r i n g a plant to maturity, to activate and u t i l i z e the carbohydrates a v a i l a b l e , and the a c t i v a t i o n i s considered to be due to a factor, f a c t o r s , hormones, or growth inducing agents formed i n most abundance where there i s an optimum photoperiod, then these  may,  also, be said to be products of l i g h t ; and though, i n one p a r t i c u l a r sense, i t i s l i g h t i t s e l f which i s needed, yet, i n the f i n a l analysis, i t i s the products of that l i g h t which are required. I t i s known that l i g h t controls plant growth and structure (22 ). a  In view of the most recent information, t h i s can hardly be denied. What one desires to know i s how l i g h t , and variations i n i t s supply, produce such profound e f f e c t s .  Tincker (2?) adopted the very simple technique of running plants,' growing i n pots, i n t o and out of a dark shed f o r only s i x , nine, or other similar periods of daylight per diem.  Under these conditions  a bean plant, normally growing to a height o f two f e e t , altered profoundly i n growth and turned into a rosett of leaves. fattened out l i k e a small carrot, and proved edible.  The root  A new  vegetable d i s h had been discovered. Light, though necessary to growth, paradoxically checks growth. Stems i n f u l l l i g h t are shorter, though dry weight i s greater, than i s the case when plants are grown i n p a r t i a l shade (22b).  Also, although  chlorophyll, necessary to a l l continuous growth, cannot be formed i n the absence of l i g h t , chlorophyll i s continuously destroyed by l i g h t . Since l i g h t controls the growth, and, hence, the structure of plants, v a r i a t i o n i n supply should a f f e c t plant structure  profoundly.  TinckerJs experiment with the bean, already described, bears out t h i s statement.  Blakeslee, East, and Clausen i n America, Maximov i n Russia,  and Tincker i n England have obtained i n t e r e s t i n g r e s u l t s by submitting plants to daylight periods of abnormal lengths.  A greenhouse technique  f o r b r i n g i n g about variations i n the lengths of days (24) has been worked Out i n great d e t a i l . There are many factors vovering growth and the production of tissues;  but the r e l a t i v e value of any one i n a p a r t i c u l a r process  can only be determined by keeping the others constant. In general, only about 1 per cent of the t o t a l energy incident on a leaf i s used i n photosynthesis ( i d and 22c).  This i s due to the  f a c t that rays o f only c e r t a i n parts o f the l i g h t spectrum are absorbed  - 33 by chlorophyll, and the photosynthesis i s limited  by the quantity of  chlorophyll, temperature and enzyme a c t i v i t y , humidity, atmospheric pressure, nutrient supply, s o i l water content, available carbon dioxide, and possibly other factors (22d).  An increase i n carbon  dioxide, i n the atmosphere means an increased d i f f u s i o n gradient of t h i s gas towards the l e a f .  Careful experiments have shown that plants  can use g r e a t l y increased percentages of carbon dioxide i f they are available.  Increasing carbon dioxide increases the y i e l d s of many  crops 30 to 300 per cent ( l e ) .  The vaporization of water i n  transpiration, and r a d i a t i o n to the atmosphere, dissipates excess energy f a l l i n g Upon the l e a f .  Most plants carry on photosynthesis at a  maximum rate, f o r usual conditions, i n a l i g h t i n t e n s i t y much below that of normal daylight.  More l i g h t may be used, of course, i f  changes occur i n determining factors. For any p a r t i c u l a r set of conditions, duration of daylight determines the t o t a l amounts of carbohydrates made.  I t i s thought  that the development of flower buds i s conditioned by the carbohydrate supply i n store at the time of t h e i r formation. that t h i s , also, influences f r u i t set (3).  Withrow has thought  She has, also, thought  that an i n i t i a l increase of carbohydrates, brought about during the e a r l y days of growth through increased photosynthesis, due to i r r a d i a t i o n from a r t i f i c i a l l i g h t , w i l l increase f r u i t s e t t i n g by improving p o l l i n a t i o n .  Whether i t Is possible f o r s u f f i c i e n t  carbohydrates to be stored during i n i t i a l growth to influence any sort of growth function l a t e r on i s extremely debatable.  I t i s known  that, at the f r u i t i n g phase, there should be an excess of carbohydrates over an ample supply of nitrogen; but A l i c e P. Withrow's own  experiment  shows, that, providing a reasonable balance be maintained between carbohydrates and nitrogen, s u f f i c i e n t carbohydrates are manufactured to provide f o r f r u i t production even with shorter days and lowered light intensity.  The f a c t that plants grown i n normal winter daylight,  when stimulated by hormone sprays to set f r u i t , produced greater crops than i n i t i a l l y i r r a d i a t e d plants, shows that there were s u f f i c i e n t carbohydrates present under normal conditions to provide for f r u i t i n g and that, though carbohydrates were low, the chemical caused the u t i l i z a t i o n to such an extent that these plants produced more f r u i t than plants with a greater carbohydrate content. Even i n winter the tomato puts f o r t h numerous, sturdy f r u i t buds which seldom f a i l to flower.  Knowing these things, i t would  appear contradictory to explain f a u l t y f r u i t setting on n u t r i t i o n a l grounds, providing the carbohydrate and nitrogenous compounds are i n a proper r e l a t i o n s h i p f o r the phase which the plant has reached. Undeniably there is,during short days, at t h i s point, a f a i l u r e i n the reproductive phase.  Tomatoes appear to flower under most conditions.  The d i f f i c u l t y i s f a i l u r e of the maturation process to continue during the short,  days of winter.  Withrow* s plants, given an i n i t i a l  i r r a d i a t i o n treatment, set more f r u i t than untreated plants growing i n normal winter daylight, but not so much as plants whose flowers had been sprayed with indolebutyric acid.  Hence, the f a i l u r e to set f r u i t  s a t i s f a c t o r i l y , i n winter, may not be due to a lowered storage of carbohydrates i n stems, but to the f a i l u r e of some other factor, or f a c t o r s which are necessary to the u t i l i z a t i o n of the carbohydrates which are present.  This does not mean that an increased y i e l d could  - 35  -  not be obtained i f carbohydrates were increased by longer duration of l i g h t , or an increased amount of carbon dioxide i n the atmosphere; always providing the u t i l i z a t i o n factor i s present; and always providing the balance with nitrogen i s maintained at a proper  ratio.  Such conditions can lead to larger y i e l d s i n any season.  The  point one wishes to emphasize i s only that, always, there must be some f a c t o r present to make possible the u t i l i z a t i o n , to make available, f o r the reproductive phase, the carbohydrates plant.  I t may  i n the  only be that the factor brings about increased f r u i t  get by increasing the v i a b i l i t y of pollen; the carbohydrates, perhaps, being used i n f r u i t production i n any case once the f r u i t i s set. , L i t t l e i s yet known regarding t h i s . Many plants w i l l not flower, or flowering w i l l not set f r u i t excepting under or near to t h e i r optimum l i g h t conditions. conditions d i f f e r with each plant.  These  Extensive information i s now  available as to various day-length requirements.  The same, or better,  e f f e c t s can often be obtained by spraying flowers with various stimulating substances. photoperiodism,  In view of t h i s information regarding  i t has been concluded that the u t i l i z a t i o n factor,  already mentioned, i s l i g h t , i t s e l f , of a d e f i n i t e duration for each plant, or a substance or substances formed, or induced to form because of l i g h t provided by day-lengths within f i x e d l i m i t s .  Many  investigators b e l i e v e terminal buds to be the l o c i for the stimulus of photoperiodism.  Cajlachjan, the Russian investigator, considers  leaves to be the receptive areas.  Thus, flowering and f r u i t i n g seem  to depend upon an optimum photoperiod.  The nearer the day approaches  - 36 t h i s the better carbohydrates are u t i l i z e d f o r reproduction and, i t may well be, the better a l l In  foods are u t i l i z e d f o r the same processes.  other words, the greater the amounts u t i l i z e d of the materials  which are necessary to reproduction and maturation.  Though excess  carbohydrates over nitrogen are necessary f o r the reproductive phase, no amount of increase i n carbohydrates, i n themselves, can cause f r u i t to  set without the u t i l i z a t i o n or stimulating factor ( s ) . The cosmos  i s a short-day plant.  Daring long-day periods, the cosmos should  be able to develop s u f f i c i e n t carbohydrates f o r any functional purpose; but i t w i l l not flower then, no matter what the carbohydrate nitrogen r a t i o .  I f the growing t i p s of the cosmos are covered with  black caps, so as to shorten the day, the treated buds w i l l flower. With just the t i p s covered, plants should s t i l l manufacture as much, or  almost as much carbohydrates as plants with uncovered buds,  providing these l a t t e r plants are subjected to the same photoperiod. If  increased carbohydrates are needed i n the covered buds to make them  flower, there i s nothing to prevent translocation of these materials from other parts of the plant, which, being s t i l l subjected to a long day, t h e o r e t i c a l l y should, and probably do have them i n abundance. The fact that the whole plant w i l l flower when deprived of the excess, by a short day, indicates that, i n t h i s plant at l e a s t , a shortage of  carbohydrates does not i n t e r f e r e with satisfactory f e r t i l i z a t i o n .  In  f a c t , the conditions developing excess carbohydrates prevent  flowering i n the cosmos. These f a c t s delineate two things:  F i r s t , that the effect of  day-length i s l o c a l i z e d and, secondly, that the effect i s caused  - 37 by l i g h t , and not by food relationships within the plant.  A l l of t h i s  appears to be a refutation of the hypothesis that a low carbohydrate content i s responsible f o r poor f r u i t set i n the tomato.  I t may  be  noted again that Withrow has shown i n her own experiment that, where there i s poor f r u i t set, the plant may be, at the same time, capable of flowering, and capable of producing f r u i t i f stimulated by hormones.  I f the plant can flower, and produce parthenooarpic f r u i t ,  why i s there a f a i l u r e i n the f e r t i l i z a t i o n process?  The f a i l u r e  appears to be due to one factor, a too short photoperiod. Flowering implies v a s t l y increased r e s p i r a t i o n .  Light i s not  d i r e c t l y necessary to r e s p i r a t i o n , f o r i t takes place i n the dark as well as i n the l i g h t .  By deduction then,light, i t s e l f i s not the  u t i l i z a t i o n factor we have spoken of. meristematic regions;  Hormones are found i n the  They are found i n greatest amounts when the  plant i s subjected to i t s optimum photoperiod. respiration locally.  Hormones stimulate  Hence, i t i s l o g i c a l , i n our present state of  knowledge, to believe that these hormones are formed,or gather, as a r e s u l t of optimum photoperiods, and they are the stimulators of plant maturation which we have been seeking. In the case of phototropism, the growth substances appear to be repelled by l i g h t , f o r they are found on the side of the stem away from the l i g h t . case?  Does l i g h t stimulate t h e i r production i n t h i s  I t i s not purposed, i n the present paper, to attempt  an  explanation of problems of t h i s nature; but r e f e r r i n g to the point serves to emphasize the fact that the problem of photoperiodism and  - 38 f r u i t set i s , a f t e r a l l , complex i n the extreme; and i t behooves anyone to think well before c a t e g o r i c a l l y challenging the conclusions of others. A l i c e P. Withrow's experiment seems to show that hormones may be stored.  Her i r r a d i a t e d plants, subjected to a.long day, i n the  e a r l y stages of t h e i r growth, l a t e r produced more f r u i t s than plants subjected to normal, winter day-length  ; but there was  a gradual  f a l l i n g o f f of the i n i t i a l increase i n f r u i t setting, showing that, though the i r r a d i a t i o n was not maintained, the effect was though gradually diminishing.  The effect was  prolonged,  explained as being  due to an increased storage of carbohydrates r e s u l t i n g from a longer duration of photosynthesis.  By now,  i t should be apparent that  there i s l i t t l e l i k e l i h o o d of t h i s being the true explanation. Vifhere hormone production i s continuously maintained a f a l l i n g off i n f r u i t s e t t i n g may be due to an exhaustion of stored carbohydrates or an exhaustion  of previously stored hormones.  In t h i s l a t i t u d e  there i s always a f a l l i n g o f f as the changing seasons carry a plant past i t s optimum photoperiod. various t o x i c chemicals, act  i n small dosages, applied to a plant,  to stimulate r e s p i r a t i o n . Hence, one may. apply various organic  acids, or hormones synthesized i n the laboratory, or hormones extracted from plants, and get the same e f f e c t s as result from the manufacture of hormones within a plant. It has been found that there i s an increase i n soluble organio materials i n plants at the point of a p p l i c a t i o n of growth promoting  - 39 substances (6).  This i s also true i n the case of growing t i p s  subjected to optimum l i g h t duration; and growth promoting substances have been isolated there. In the case of the a r t i f i c i a l a p p l i c a t i o n known hormones maybe applied, and c e r t a i n organic acids which may,  or may not be  hormones themselves; i * e . , i n the sense that they stimulate t i s s u e changes d i r e c t l y .  These organic acids, i f they are not hormones, may  only cause hormones, manufactured i n the plant* to migrate to the point of a p p l i c a t i o n . These are matters which s t i l l require study. However, there seems l i t t l e doubt that the reproductive phase i n a plant i s not so much influenced by t o t a l photosynthesis, and food relationships within a plant, as i t i s by some factor or f a c t o r s , a c t i v a t i n g the u t i l i z a t i o n of foods f o r c e r t a i n , d e f i n i t e purposes; and the f a c t o r , or factors seem to be related to optimum day-length. Experiment has shown that substances present i n growth regions, and, present i n the greatest abundance during optimum daylight conditions, may be used to produce growth e f f e c t s when applied a r t i f i c i a l l y . Growth, p a r t i c u l a r l y reproductive growth, implies increased respiration ( ^ ) .  The rate of r e s p i r a t i o n i s affected by the amount  2  of a v a i l a b l e carbohydrates*  temperature, oxygen, and water.  concentrations of t o x i c chemicals, such as ether, chloroform, paraldehyde, may  Weak and  speed up the rate of r e s p i r a t i o n f o r a time, and  b r i n g plants into flower e a r l i e r .  Injury and disease also increase  r e s p i r a t i o n , taking sugars to injured portions f o r purposes o f repair. Increased temperatures within opening flowers may be as much_as degrees Centigrade  (If).  30  Thus, i t maybe, that when the reproductive  -40-  phase i s reached, anything increasing r e s p i r a t i o n may he a f a c t o r i n causing the process to continue to completion. plant i s enzymatic i n nature.  Respiration i n the  This i s a t h i n g to he remembered.  How  i s i t t i e d i n with the effects of growth regulators such as hormones? Are the l a t t e r organic c a t y l i s t s also? Vitamins, synthesized by the plant, seem, also, to be important to the health and growth,of the plant.  Probably they are  always present, unless the plant i s temporarily out of i t s environment, as i t i s when i t has just been transplanted. Their a r t i f i c i a l feeding may be expected to give best r e s u l t s under such conditions.  The same,  of course, may be said of hormones. Temperature i s one of the more important factors i n plant growth.  Each plant has an optimum f o r each phase of i t s growth,  u s u a l l y requiring a higher temperature f o r the maturation phase. Temperature influences the a c t i v i t y of enzymes. The r e l a t i o n of amounts of carbohydrates and nitrogen i s one of the very important things to be considered i n plant growth.  The  r e l a t i v e proportions of carbohydrates, f a t s and o i l s , and proteins may be maintained i n a p a r t i c u l a r r a t i o by varying the amount of soluble nitrogen compounds fed the plant; so that nitrogen i s brought into l i n e with the amount of carbohydrates being formed by photosynthesis. Let  be excess or abundant carbohydrates, Nf- be excess or  abundant nitrogen, C ample carbohydrates, N ample nitrogen, c r e s t r i c t e d carbohydrate supplies, and n r e s t r i c t e d nitrogen supplies, then, normally, the r e s u l t s are: c, N/  Poor growth.  Small amount of f r u i t .  Nitrogen not a l l u t i l i z e d  with carbohydrates i n the synthesis of higher organic compounds.  41  C N  Of  Bank growth.  -  Small amount of f r u i t .  Just enough of  carbohydrates so that nitrogen i s f u l l y u t i l i z e d . Pair growth.  Good f r u i t i n g .  Poor growth.  Small anount of f r u i t .  (2)£  n That l i g h t i s a potent influence on plant structure i s seen i n the fact that plants grown f o r a time i n the absence of carbon dioxide, hut i n the presence of l i g h t , do not become  e t i o l a t e d ( i g ) . In addition  to an optimum day-length there i s an optimum l i g h t i n t e n s i t y f o r a plant, seen i n the fact that some plants prefer f u l l l i g h t , while others prefer shade.  These optimum l i g h t conditions seem necessary to normal  t i s s u e d i f f e r e n t i a t i o n ; p a r t i c u l a r l y so i n the case of tissues.  reproductive  F r u i t s e t t i n g appears to be at a maximum  in a light intensity  exceeding that required for maximum photosynthesis.  I t i s possible that  c e r t a i n organic acids, applied to the outer surfaces of flowers, not only induce the s e t t i n g of parthenocarpic  f r u i t s , but may  may  induce  maximum f r u i t s e t t i n g , even during a wide departure from optimum l i g h t conditions.  To obtain ideal l i g h t conditions by a r t i f i c i a l i l l u m i n a t i o n ,  an a l t e r n a t i v e method, may be found most d i f f i c u l t . It i s possible that even under an optimum day-length a plant f a i l to flower i f the l i g h t i n t e n s i t y i s too weak.  may  The f a i l u r e here  may be due to both f a i l u r e of the u t i l i z a t i o n stimulus and to i n s u f f i c i e n t photosynthesis.  In both long and short-day plants vegetative growth i s  greatest under the. long day.  The difference i s that, i n the plant  p r e f e r r i n g the long day, reproductive a c t i v i t y i s also great.  - 42 A c t i v a t i o n of any process i n a plant "by day-length, or a r t i f i c i a l l y applied chemicals, may has been removed.  This may be why  continue a f t e r the  stimulus  the i r r a d i a t e d plants i n A l i c e  P. Withrow's experiment gave increased f r u i t production a f t e r the i r r a d i a t i o n was  discontinued.  There appears to have been a  gradually diminishing e f f e c t .  "The  reaction or response of a plant to a stimulus may  u n t i l some time a f t e r the stimulus i s applied and may a f t e r the stimulus i s removed.  H  not begin continue  (ih).  F i n a l l y , the actual growth of plants r e s u l t s from the simultaneous operation of a l l f a c t o r s , i n t e r n a l as well as external. It i s therefore, not always possible to separate the influence of a single factor from that of the other f a c t o r s .  DISCUSSION OP A RELEVANT EXPERIMENT The work of several experimenters has already been ^briefly.' reviewed i n t h i s paper.  A paper e n t i t l e d "Comparative E f f e c t s of Radiation  and Indolebutyric Acid Emulsion on Tomato F r u i t Production", and written by A l i c e P. Withrow of"Purdue U n i v e r s i t y A g r i c u l t u r a l Experimental Station, Lafayette, Indiana,  (3),  describes a greenhouse experiment which i s  c l o s e l y p a r a l l e l e d , i n many respects, by the present investigation. Because of t h i s , and because the r e s u l t s of the Lafayette experiment and the present experiment follow the same general pattern, i t i s i n t e r e s t i n g t o attempt an i n t e r p r e t a t i o n of the r e s u l t s of the former from a p h y s i o l o g i c a l viewpoint. A l i c e P. Withrow worked with three groups of tomato plants of two v a r i e t i e s , Long Calyx, and Michigan State Forcing, sown December 15,1943. While i n seed f l a t s , one group was  i r r a d i a t e d f o r twenty^one days from  the time of the unfolding and greening of the cotyledons.: ... I r r a d i a t i o n was f o r four hours dailyffimVa 300 watt internal r e f l e c t o r lamp.' On January 14, a l l plants were transplanted' to ground beds.  The  three groups were: (a) Control plants grown by regular greenhouse methods, and vibrated d a i l y , a f t e r flowering, to a i d p o l l i n a t i o n . (b) The plants given i n i t i a l i r r a d i a t i o n and,  subsequently, the  same treatment as the control plants. (c) Plants whose flowers were treated four times a week withja growth regulator, indolebutyric acid,ZfacnpipvraV-f rc*"%inasal'atomi-aer'. ^ t h o u g h  no precautions were taken to prevent p o l l i n a t i o n , these plants were not vibrated to a i d i t . The i r r a d i a t e d plants showed an increased f r u i t set on the f i r s t f i v e c l u s t e r s f o r Long Calyx, and on the f i r s t four c l u s t e r s for Michigan State Forcing. for  Beyond t h i s the production was l e s s than  comparable c l u s t e r s of the control plants.  The net r e s u l t was,  that Long Calyx showed a 10 per cent t o t a l gain i n the number, and 9 per cent i n the t o t a l weight of f r u i t s over the controls; and Michigan State Forcing a 3 per.cent gain i n each of these.  The average  weight per f r u i t was about the same as f o r the control plants. It i s possible, i n the case of these i r r a d i a t e d plants, that the l i g h t treatment, given when the plants were small, brought about a storage of hormones which l a t e r , on f i r s t flower c l u s t e r s , stimulated an excess of f r u i t set over that i n controls.  Perhaps the decrease  i n f r u i t set on l a t e r c l u s t e r s , as compared with controls, was due to a more rapid i n i t i a l u t i l i z a t i o n of available carbohydrates i n the i r r a d i a t e d plants, with a subsequent exhaustion of stored hormones, arid a greater i n i t i a l exhaustionnoiP carbohydrates.  The fact that the  i r r a d i a t e d plants showed a small net gain may be due to a better t o t a l u t i l i z a t i o n of carbohydrates.  Even i f the small amount of  increased carbohydrates i n the t i n y plants i r r a d i a t e d i n the f l a t s , did  influence l a t e r f r u i t setting, i t i s doubtful i f the increased  carbohydrates would be s u f f i c i e n t to explain the net gain i n weight of fruits.  The explanation i s more l i k e l y to hinge upon a storage of  stimulating substances within the plant during the period of initial  irradiation.  -  45  -  Irradiated plants were out of production e a r l i e r than control plants, due to the f r u i t i n g phase proceeding at a faster rate.  F r u i t s matured more r a p i d l y . ' P r e - i r r a d i a t i o n d i d not ensure adequate p o l l i n a t i o n , as  many blossoms f a i l e d to set f r u i t . Irom observations made during the present  experiment,  seedlings during i n i t i a l i r r a d i a t i o n grow more r a p i d l y than control plants.  Probably extra carbohydrates, made by additional photosynthesis,  are u t i l i z e d immediately i n growth, and not stored to influence f r u i t set,  as intimated i n Withrow*s introduction.  In any case, there i s no  accumulation f o r the formation of f r u i t buds i n a plant u n t i l vegetative growth slows down or, even, has ceased. Where plants were treated with the growth regulating substance, there was,  on Long Calyx, a net increase of 18 per cent i n number of  f r u i t s set, and 15 per cent i n weight over controls. Michigan State Forcing were about h a l f t h i s .  Increases f o r  The i n i t i a l increase on  Long Calyx, on the early c l u s t e r s , where increase was greatest, was not followed by a decrease to a lower l e v e l than controls, as was the case with the i r r a d i a t e d plants; although, l a t e r , as the season advanced, weight production came to equal that of control plants; not because of a drop i n production i n the treated plants, but because of an increase i n production i n control plants as the days became longer, and approached more nearly the optimum requirements of the tomato.  Thus, as Withrow  has l o g i c a l l y suggested, i t appears, from t h i s experiment, that the use ^ of growth promoting substances, on the flower of the tomato, may not be worthwhile on the l a t e r flower clusters, as the production was not  - 46 increased over that of controls when the weather became brighter and the days longer.  Thus, i t i s shown that the a r t i f i c i a l a p p l i c a t i o n  i s only e f f e c t i v e where the plant i s out o f i t s optimum reproductive environment during the short,winter days.  Later, as longer days  b r i n g about the production of growth stimulating substances within the plant, the continued a p p l i c a t i o n of growth promoting substances, a r t i f i c i a l l y , does not increase the effect of those manufactured n a t u r a l l y inside the plant; but, on the contrary, has no effect whatsoever. The average weight of f r u i t s from plants sprayed with the growth regulator was observed to be less than that f o r the control plants, though about the same number of f r u i t s were set as on - - - -  control plants.  ~f  This seems to imply that, while plants growing  n a t u r a l l y had the benefit of a c e r t a i n amount of carbohydrate storage before f r u i t i n g , t h i s was l a c k i n g i n plants which had already been producing f r u i t during the short days.  Nevertheless,  the net increase  displayed by a r t i f i c i a l l y treated plants shows that the procedure i s worthwhile.  ,  Beyond mentioning that the plants treated with the growth regulator often had f r u i t s with a green placental pulp, there was no other reference made to the e d i b i l i t y of f r u i t . Plants treated with a growth regulator showed a greater net increase i n production over controls, p a r t i c u l a r l y i n f i r s t c l u s t e r s , than d i d i n i t i a l l y i r r a d i a t e d plants, showing that increased carbohydrates were not needed f o r increased f r u i t production, and  - 47  -  therefore that there was very l i t t l e likelihood that they were needed for increased fruit set. Plants treated with the growth regulator could have had no more carbohydrates as a result of photosynthesis'than oould plants used as controls. It is most probable that i f an experiment were to be conducted so that sugars were introduced into a plant artificially in the absence of long day photosynthesis; i.e., during short days, there would s t i l l be no fruit setting, even with the increased amounts of carbohydrates, i t being almost indisputable that the main factor in fruit setting is the accumulation of growth substances due to a long day, or to the application of such substances artificially, Also, i f Withrow's experiment were conducted so that plants irradiated in the flat grew in an atmosphere of lessened carbon dioxide supply, so that there would be less carbohydrates than in the control plants, i t is probable that the irradiated plants would s t i l l show an increased fruit set and production over controls. A major conclusion to be drawn is that the effects of artificially applied treatments differ greatly with varieties; but that treatment with a growth regulator during short days does result in important increases in fruit set in the tomato plant of the two varieties grown in the experiment.  - 48 MATERIALS AND METHODS OF THE FIRST YEAR On October 30, 1946, tomato seed of the variety Vetomold 121 was  sown i n s t e r i l e , washed, r i v e r sand on moisture r e t a i n i n g  burlap sacking i n two f l a t s , 12 by 18 by 3 inches i n s i z e .  The use  of t h i s coarse sand, of p a r t i c l e size 2,0 to 0,2 millimetres, would, i t was hoped, lessen damping o f f i n seedlings.  The seed  was placed i n shallow, l a t h made rows 1.5 inches apart, and l i g h t l y covered with s i f t e d sand.  The sand was watered u n t i l i t was  thoroughly moist, covered with newspapers, to exclude l i g h t ; and the l a b e l l e d f l a t s placed i n the semi-tropical room, of the u n i v e r s i t y greenhouse, on sand covered propogating benches receiving a bottom heat of 7 0 degrees Fahrenheit from hot water pipes.  The sand i n  the f l a t s was watered whenever i t showed signs of drying out. This was every second  day.  On November 5» 1946, the f i r s t cotyledons appeared; and the newspapers were removed.  Though mice were present, they were kept  under control by the use of ordinary traps; so that there was  no  rodent damage to seedlings at any time. On November 8, f l a t B was placed i n the plant n u t r i t i o n room, where the temperature was maintained between 6 0 and 6 4 degrees Fahrenheit-.  A 200 watt fluorescent lamp, regulated automatically  by an e l e c t r i c clock, was suspended two feet above the tops of the seedlings, which were i r r a d i a t e d f o r twenty-two days f o r four hours d a i l y , the periods being 4:00 8 :30 p.m.  a.m.  to 6:00  a.m.,  and 6 : 3 0 p.m.  to  .The cost of providing the l i g h t was four cents per K. W.  H.  -  49  -  According to H i l l , Overholts and Popp, when plants receive alternations of l i g h t and darkness i n periods of six hours or l e s s , they respond as though kept under a long day ( 1h ).  To test t h i s out,  four seedlings i n f l a t B were covered with black paper "caps d a i l y , excepting on Sundays, from 8:15 a.m. u n t i l f i f t e e n minutes past noon, or f o r a period of four hours each day f o r s i x days i n the week.  This,  with the hours of a r t i f i c i a l l i g h t i n g already stated, f u l f i l l s the conditions above.  I t was anticipated, that? i f the statement should  prove to be correct, these covered plants, though undoubtedly producing less carbohydrates as a r e s u l t of photosynthesis, should respond with a percentage of f r u i t setting as great as i n the uncovered plants. # This group, of four plants, was l a b e l l e d Pa; the l e t t e r P s i g n i f y i n g the large group receiving a pre-treatment i f i r r a d i a t i o n ; and the l e t t e r a * s i g n i f y i n g the covered test group within i t . f  The d a i l y capping of the group Pa was stopped at the same time as the i r r a d i a t i o n of a l l the plants i n f l a t B; i . e . ,  after  twenty-two days. Plat A, on November 8, was placed under the normal greenhouse daylight conditions of the h o r t i c u l t u r a l research room, which was kept at a temperature of 52 to 54 degrees Fahrenheit during the coldest months.  As the season advanced, t h i s minimum degree of  warmth was greatly increased, u n t i l , at flowering time, i t was often over 80 degrees. From November 7, u n t i l the time when the seedlings were #  I t i s now thought (1948) that a long day can be simulated by d i v i d i n g or interrupting a long dark period with one minute of a r t i f i c i a l illumination, H. A. Borthwick ( 21 ).  -  50 -  were transplanted into s o i l , they were fed with a nutrient solution applied s u f f i c i e n t l y often to keep damp the surface of the sand i n the  flats. The solution used was Hoagland's and Arnold's, 1 9 2 8 .  The  s i x major elements were provided from molal stock solutions (1 I or 1 GMW)of solute per l i t r e of solution) made up i n d i s t i l l e d  watery  using each of the following i n chemically pure form: Potassium phosphate, { KHg P 0 ) ; 4  potassium n i t r a t e ,  { KHO^ );  calcium n i t r a t e , ( C a i : ( N 0 j ) 2 . 4 H 0 ) ; 2  magnesium sulphate, (MgSo . 7H2O ) . 4  The e s s e n t i a l element i r o n (Fe) was provided from a stock s o l u t i o n of a Iper cent concentration of i r o n t a r t r a t e . The table below shows, succinctly, the proportion of each stock solution applied to the plants i n one l i t r e of nutrient solution: FOB USE IN 1 1 . OF NUTRIENT  STOCK SOLUTION  SOLUTION ' (1.)  1 M . KH P0^  1 c.c.  2  (2.)  KNDij  (?.)  Ca(N0 )2.4H D  5 c.c.  (4.)  MgS0 .7H 0  2 c.c.  (5.)  5 c.c. 3  4  2  2  Iron Solution  1 c.c.  In addition, to provide the micro elements, boron, magnanese, zinc and copper^ were mixed together i n a pint of distilled  water, one-fourth teaspoonful of each of the following  substances being the sources of the elements:  Boracic Acid.HjBCj manganese sulphate zinc sulphate ,  ?  MnSO^, 4H2O  ;  ZnS04.7H20  ;  copper sulphate, CuS0  4  5H2O ,  This mixture was used at the rate of ten drops per l i t r e of Hoagland's solution. A l l stock solutions were stored i n glassware i n a dark cupboard, Such solutions are best applied when they have an a c i d i t y of approximately pH6.  In practice, the nutrient solutions are mixed i n  d i s t i l l e d water without adjustment. s o i l solution of pH 6 or 6 . 5 ;  However, the tomato prefers a  so t h a t , . i f i t i s grown to maturity i n  s t e r i l e sand, a l k a l i n g solutions may be adjusted by the addition of a few drops of a c e t i c , or of sulphuric acid.  Under a l k a l i n e conditions,  i r o n goes out of solution, r e s u l t i n g i n the tomato, i n c h l o r o s i s ^ Available i r o n may be supplied by spraying f o l i a g e with a solution of i r o n sulphate. Solution plants have well controlled conditions, and are l a r g e l y free of disease, insect pests, and weeds. A l l seedlings were thinned out to a spacing of 2 times 2 inches on November 1 8 . I r r a d i a t i o n of the seedlings i n f l a t B was terminated November 3 0 , 1946.  On t h i s date, twenty-five  appearance of the f i r s t cotyledons,  days a f t e r the  f i f t y - s i x plants were selected and  transplanted into 2 inch, earthern pots containing a sandy, composted s o i l based on rotted grass cuttings.  U n t i l the time of transplanting  52 into 10 inch, pots, these plants were watered with the solutions used i n the f l a t stage.  Twenty plants, as uniform i n size as possible,  were taken from the i r r a d i a t e d group.  Included were the four  plants of group Pa, which had been subjected to simulated day conditions of l i g h t .  long  T h i r t y - s i x uniform, untreated plants  were selected from f l a t A. Sixteen of the plants from f l a t A were placed i n the plant n u t r i t i o n room with 200 watt fluorescent lamps suspended 24 inches above t h e i r tops.  I r r a d i a t i o n was given f o r s i x hours d a i l y ;  three  hours i n the morning, ending at sunrise; and three hours i n the evening commencing at sunset.  The times of sunset and sunrise  were determined from l o c a l newspapers. increased  The effect was a g r e a t l y  photoperiod.  The remaining f o r t y plants were placed, on a long bench, under the normal daylight conditions of the somewhat cooler h o r t i c u l t u r a l research room. It has been thought that a hormone spray on f o l i a g e , p r i o r to flowering, might induce f r u i t setting, providing a concentration could be found which would be s u f f i c i e n t l y d i l u t e to avoid the danger of causing epinasty, yet strong enough to be effective.  To date, no success has been attained.  Nevertheless,  the four plants i n group S were set aside f o r such a t e s t .  -  5} -  A l l plants were l a b e l l e d .  The tabulation below i s  self-explanatory.  Group  Ho. of Plants  H NT  Treatment  8  (Control Group) Normal Daylight  8  Normal Daylight and Indolebutyric Acid  P  8  Pre-irradiation.No Hormone Treatment  PT  8  Pre-Irradiation and Indolebutyric Acid  Pa  4  Pre-Irradiation and Simulated Long Day  S  4  Normal Daylight and F o l i a r Sprays  L  8  Photoperiod increased by Six Hours Daily I r r a d i a t i o n . No Pre-Irradiation  LT Total On January earthenware pots.  8  As above, and Indolebutyric Acid  56  7» 194-7,  a l l plants were transplanted to 10 inch,  L a b e l l i n g and room locations were not changed.  The s o i l used was s i m i l a r to that i n the f i r s t transplanting. Using a colorimetric determination  f o r pH, and rapid s o i l t e s t i n g  - 54 methods, the condition of the s o i l was found to he CNJ P4 KJ; i . e . , the pH was between 5 and 6, available n i t r a t e s were i n medium supply, phosphorous was low, and potash medium.  The supply of calcium, also,  was found to be medium. The requirements of the tomato are C N2 P2 K3; i . e . , pH 5 to 6, and a high proportion of each nutrient. Well rotted animal manure was sieved through a % inch r i d d l e . One pound of the material was added to each pot.  One-half, a coarse  portion, was mixed with s o i l near the bottom of the pot.  In t h i s  p o s i t i o n i t was a reservoir of moisture, and was a v a i l a b l e f o r plant feeding at f r u i t i n g time, when roots had reached t h i s depth.  A fine  portion of the manure, along with a tablespoonful of Urbanite 6-7-6, a product of the F e r t i l i z e r D i v i s i o n of Canadian Industries, Limited, was thoroughly mixed i n the upper layer of s o i l f d r immediate  feeding.  The tomatoes were planted at a somewhat greater depth than that at which they had been growing i n the small pots, and u n f e r t i l i z e d s o i l heaped-around them to prevent i n j u r y from the commercial mix.  They were pressed f i r m l y into the s o i l , and a  cupful of warm water poured around them. B i o l o g i c a l l y , the s o i l analysis was. borne out at each stage of the p l a n t s development.  Just s u f f i c i e n t nutrients had been  added to correct the o r i g i n a l d e f i c i e n c i e s .  As the added nutrients  were slowly available throughout the season, no further s o i l treatment was found necessary.  However, i r o n t a r t r a t e solution was applied  once each month as a precautionary measure, as iron i s commonly d e f i c i e n t .  -55 Two  -  weeks l a t e r a stake was pushed into the s o i l of each pot  and,- as increased growth made i t necessary, the plant was  t i e d to t h i s .  To minimize variations i n l i g h t and heat i n t e n s i t y , due to placement, the plants of a l l groups were randomized over the s i t e , rather than kept i n separate rows. Cultural treatment, i n general, was as uniform as possible. Watering was done i n such a fashion as to prevent the s o i l around the roots becoming e n t i r e l y dry at any time. A l l plants were trained to single stems. On January 28, the four plants of group S were sprayed on f o l i a g e and stems, u n t i l wet but not dripping, with varying concentrations was  of indolebutyric acid i n d i s t i l l e d water.  f i r s t dissolved i n 95 per cent ethyl alcohol.  concentrations  The a c i d  The  applied were: 50 p.p.m. on plant SI, 100 p.p.m. on plant S2, 250 p.p.m. on plant SJ, 500 p.p.m. on plant  S4.  On January JO, when t h e i r photoperiod had just commenced to r i s e above f i f t e e n hours, the plants of groups L and LT formed f i r s t c l u s t e r flower buds, some of which started to open.  As the day length rose towards  sixteen hours, these opening buds closed, but remained persistent. of the flowers opened f u l l y .  After February 7,  when the photoperiod had  reached f i f t e e n hours, t h i r t y minutes, no more buds formed, and plants continued vegetative growth only.  None  the  I t was thought that the  photoperiod had perhaps become excessive f o r flowering, so that, on February 21,  when the normal day had reached ten hours,  It i s now believed (1948) that these effects were due to the q u a l i t y of the fluorescant l i g h t supplied. The number of days of exposure to t h i s l i g h t seems, also, to have been a f a c t o r .  -  56 -  twenty-nine minutes, and the extended day sixteen hours and twentynine minutes, a l l plants of L grouping (L, and LT) were moved to the h o r t i c u l t u r a l research room, and placed on the same bench as the plants of other groupings. Also, February 2 1 , 1947, was the date on which the f i r s t flowers of cluster i opened i n the N, NT, P, .PT; Pa, and S groups. With the beginning of flowering, those plants r e c e i v i n g no chemical treatment were vibrated, d a i l y , by cane.  tapping supporting stakes with a  The purpose of t h i s was to a i d p o l l i n a t i o n so that poor f r u i t  set would be i n d i c a t i v e only of unsatisfactory f e r t i l i z a t i o n , rather than lack of p o l l i n a t i o n . The f i r s t three clusters only were treated. used was indolebutyric a c i d i n every case. ethyl alcohol, and made up i n d i s t i l l e d  The treatment  Dissolved i n 95 per cent  water, the organic acid  ^ - ( i n d o l e - 3 ) - n - b u t y r i c acid, applied with a nasal atomizer, was used i n the concentrations 50, 100, 250, and 500 p.p.m. as a f o l i a r spray on the plants of group S; i n the concentration 0.5 per cent  (5000 p.p.m. ) as a blossom spray on the f i r s t c l u s t e r s  of the groups NT and PT; and i n a concentration of 0.01 per cent • ( 100 p.p.m. ) on the t h i r d c l u s t e r s of the same groups.  The L,  LT groups had no f i r s t c l u s t e r s , and were not treated on the t h i r d cluster because the treatment here was mainly a test of concentration effectiveness, and i t was f e l t that two groups would supply the necessary information as c l e a r l y as three groups.  - 57 The ©.5 per cent concentration of indolebutyric acid wag applied to entire c l u s t e r s as a delayed spray; i . e . , one application only was made to each cluster; and t h i s was applied a f t e r most of the flowers of the c l u s t e r were f u l l y open, with the e a r l i e r flowers on the point of dropping.  Buds and flowers a l i k e were sprayed u n t i l  thoroughly wet; the intention being to get some of the acid low down on the style, or d i r e c t l y on the ovary, wherever this, -was possible. The flowers of the second clusters of groups NT, PT, and LT were emasculated just as each was on the point of opening, and a d i l u t e concentration of indolebutyric acid i n t a l c dust applied d i r e c t l y to the ovary with a camel's h a i r brush. used was a commercial one known as Hormodin No 1.  The preparation I t i s made  by Merck and Co., Eahway, N, J , Emasculation was performed i n one, simple operation by removing the r i n g of stamens with a p a i r o f small tweezers. O r d i n a r i l y , petals and p i s t i l come o f f at the same time. Ho. groups!other.thanTthose  named were given hormone  treatmentsi Accepting the c r i t e r i o n that a f r u i t has reached the greenripe stage, anu i s ready f o r picking when a white spot shows c l e a r l y on the blossom end, twenty such f r u i t s , as they reached the designated stage,  were picked from f i r s t c l u s t e r s of group N.  A similar  number of f r u i t s , at the same stage of development, were taken from the f i r s t clusters of group NT.  In order to gain some comprehension  of the effect, of organic acid sprays on the weights of mature f r u i t s , y These were the f i r s t twenty f r u i t s , i n each group, to reach the designated stage of maturity.  58  -  -  and on f i n a l y i e l d , these two groups of green-mature f r u i t s were compared as to average weights. Records were c a r e f u l l y kept, and the following d e t a i l s noted as they were observable:  The dates of flowering f o r c l u s t e r s ; the  number of flowers i n each cluster; the treatment; the dates of treatments; the number of f r u i t s set on each cluster { taken when the ovary of a flower had noticeable increased i n s i z e ) ;  the dstes of  harvesting; the number.of.fruits harvested from each cluster; the t o t a l .weight of f r u i t on each c l u s t e r ; the diameters of f r u i t s from second clusters; the appearance and quality of the f r u i t s ; and the percentage of parthenocarpic f r u i t s set. The weights of green-ripe f r u i t s were taken as they were picked. A l l remaining f r u i t * excepting those of c l u s t e r 3 of group L, were harvested A p r i l 3, 1«947.  The weight was recorded f o r the t o t a l  number of f r u i t s on each cluster, excepting f o r the f r u i t s of the second cluster of group LT.  These were harvested to ascertain the  percentage of seedless f r u i t s formed i n the group. readings were taken f o r the f r u i t s of cluster 2.  Diameter The measurements  were taken with c a l l i p e r s at the widest part of each f r u i t at r i g h t angles to the stem-blossom axis.  Measurements were transferred  to a metric scale, and the readings recorded i n centimetres. A l l f r u i t s were cut open to ascertain the numbers which were parthenocarpic. Thus, on A p r i l 3, 1^47, the f i r s t part of the experiment was terminated.  MATERIALS AND METHODS OF THE SECOND YEAR On October 27, 1947 , tomato seed of the variety Vetomold 121 was.sown i n a f l a t of s t e r i l e , washed r i v e r sand. p l a n t i n g was similar to that followed i n 1946.  The method of  The f i r s t seedlings  appeared on November 3, 1947. A sowing of the same variety and one of A i l s a Crajfcg, were made on  November 12, 1947. In these f l a t s the f i r s t cotyledons  appeared November 17, .1947. Plants i n a l l the f l a t s were thinned out, to a spacing of 2 times 2 inches, as soon as they showed signs of being crowded. In the f l a t stage nutrients were supplied by sprinkling with the solution used i n 1946. On December 1, 1947, seventy-two plants of uniform s i z e , twenty-four from each of the three f l a t s , were selected and transplanted into 2 inch, earthen pots containing a sandy, composted s o i l .  These  plants were, also, fed with Hoagland's and Arnold's solution. Plants from the f i r s t sowing of Vetomold 121 were l a b e l l e d V 121. A.  Those from the second sowing of Vetomold were l a b e l l e d  V 121 B.  Plants of the A i l s a Craig group were marked AC.  these groups was divided into four subgroups. as follows: V 121 AC  V 121BC  ACC  V 121 Aa  V 121 Ba  ACa  V 121 Ab  V 121 Bb  ACb  V 121 Ac  V 121 Be  Ac  Each of  These were l a b e l l e d  - 60 -  Plants i n the C subgroups were controls. with hormones.  They were not treated  The subgroupings a, b, and c were treated with hormone  sprays applied to the f l o r a l parts. The seventy-two plants were placed i n randomized upon a table i n the h o r t i c u l t u r a l research room.  positions  Temperatures  were,  i n general, about as they were during the previous year. On January 5, 1948, a l l plants were transplanted to s o i l i n 10 inch, earthen pots.  Plant positions and lab e l l i n g s were unchanged.  The source and composition of the s o i l were similar to those of 1946; and the condition was found to agree remarkably well determined previously.  with that  A c i d i t y and nutrient l e v e l s were C N3 P4 KJ.  The pH was found to be 6, s l i g h t l y higher than i n 1946, but a s a t i s f a c t o r y l e v e l of a c i d i t y f o r tomato growth.  Calcium was present  i n medium amounts. As before, one pound of animal manure and a tablespoonful of Urbanite 6-7-6  W  a s mixed into the s o i l of each pot; the commercial  f e r t i l i z e r being placed i n the top layer of s o i l f o r early feeding. As growth made i t necessary, pots were staked with bamboo canes, the plants t i e d to these supports with r a f f i a , and each tomato trained to a single stem. Water was applied moderately at i n t e r v a l s so that the s o i l , at no time, became completely dry.  In order to prevent leaching of  nutrients, no excess of watering was done. Despite, differences of more than two weeks i n sowing times, and the greater size of plants i n the V 121 A group, every plant,  - 61 i n every group, opened i t s f i r s t flowers on February 23, 194-8. After flowering, a l l control plants were vibrated, d a i l y , to aid p o l l i n a t i o n , so that, as before, poor f r u i t set would be i n d i c a t i v e only of unsatisfactory f e r t i l i z a t i o n ,  and not of lack of p o l l i n a t i o n .  The plants treated with hormones were not shaken, but no precautions were taken to. avoid p o l l i n a t i o n brought about by any other means. Daring the year 194-7, indolebutyric acid 5000 p.p.m., or 0.5 per cent, was found to be e f f e c t i v e i n that i t g r e a t l y increased f r u i t set on f i r s t flower c l u s t e r s . minor amount of leaf damage.  However, t h i s concentration caused a This may have been due to an over-  vegetative condition i n the plants used.  A f o l i a r t e s t , made i n 1948,  with t h i s concentration of indolebutyric acid, produced no epinasty i n either the v a r i e t y Vetomold 121 or A i l s a Craig.  Nevertheless, i t  was decided to use the acid i n a reduced concentration range f o r the second part of the investigation.  A 0.02 per cent solution has been  shown, by Howlett, to be i n the neighborhood of the least strength producing any considerable p o s i t i v e r e s u l t s , although i t does not approach the usefulness of higher concentrations.  Therefore, a  strength of 200 p.p.m. was chosen f o r the lower l i m i t o f the spray concentration range. During 1948,  i n addition.to water sprays of indolebutyric  acid, the commercial preparations "Fix", and "Seed-Less-Set" were also applied as water-sprays to f l o r a l parts i n an attempt to increase f r u i t set. The chemicalV-(indole-3)-n-butyric  acid, dissolved i n 95  per cent ethyl alcohol, was made up i n d i s t i l l e d water to  concentrations  of 3 0 0 0 p.p.m., 5 0 0 p.p.m., and 2 0 0 p.p.m.  prepared by d i s s o l v i n g 5 t a b l e t s i n a quart of water.  "Fix" was  "Seed-Less-Set"  was made up so that one quart of a water solution contained  one ounce  of the material. Controls were not treated with hormones.  A l l other groups  were treated, on f i r s t c l u s t e r s only, with one of the hormone sprays applied with a nasal atomizer.  Each treated c l u s t e r received a  single delayed spray applied i n a f i n e mist.  As previously stated,  a delayed spray i s applied when most of the flowers i n the c l u s t e r are open, and e a r l i e r flowers are s t a r t i n g to drop.  In t h i s way  i t i s possible to treat the maximum number of buds which have enlarged to a point where a growth regulater w i l l influence t h e i r -development into parthenocarpic  fruits.  A l l groups having flowered on the 3ame date, February. 2 3 , 1948,  i t was possible to spray a l l treated subgroups on February 2 8 ,  1948.  The table below shows the material and concentration applied  to each subgroup. No of Plants V 121 Aa  Treatment  6  Indolebutyric acid 0.3 per cent  b  6  Indolebutyric acid 0.05 per cent  c  6  Indolebutyric acid 0.02 per cent  V 121 Ba  6  h  6  c  6  "Fix" Indolebutyric acid 0.05 per cent "Seed-Less-Set"  - 63 -  ACa  6  Indolebutyric acid 0.3 per cent  b  6  Indolebutyric acid 0.05  per cent  c  6  Indolebutyric acid 0.02  per cent  One gram of indolebutyric  acid was used i n 1947-1948.  Records were kept of the number of flowers and the number of f r u i t s set i n each of the f i r s t c l u s t e r s . F i r s t c l u s t e r f r u i t s were permitted to mature and were harvested as i n d i v i d u a l tomatoes ripened.  Harvesting commenced  A p r i l 14, 1 9 4 b and was completed /May.-6  1948.  Total y i e l d s  and average f r u i t weights were compared. No stress was placed upon parthenocarpy, as the attainment of t h i s was not the object i n view; but f r u i t s were examined to determine q u a l i t y . These observations completed the experimental phase of the work.  - 64 -  PRESENTATION OF RESULTS FOR THE FIRST YEAR The E f f e c t of an Excess of Fluorescent Light on the I n i t i a t i o n of Flowering i n Tomato Plants: On January 30, when t h e i r photoperiod had j u s t coranenced to r i s e above f i f t e e n hours, plants of the L groups had formed flower buds.  Some of these buds started to open; but, as the photoperiod  rose towards sixteen hours/toe* seasonal lengthening of the natural days, these buds closed again without having opened f u l l y .  After  February 7, when the photoperiod had reached f i f t e e n hours,  thirty  minutes, no more buds formed, but o l d buds persisted u n t i l the termination of the experiment on A p r i l 3,  1947.  On February;21, when the normal day had reached ten hours, twenty-nine- minutes, and the extended day sixteen hours and twenty-nine minutes, a l l plants of the % groupings { L, and LT ) were moved, to the h o r t i c u l t u r a l  research room.  Flower buds of the f i r s t  c l u s t e r already formed* did. not open, but persisted u n t i l the termination of the experiment. c l u s t e r s of L and LT, flowered.  However; on March 7,  the second  This was four days l a t e r than  the second c l u s t e r s of other groups.  The t h i r d c l u s t e r s of both  groups flowered March 12, which was the date of flowering of a l l other groups. I t should be noted that while control plants, subjected to a normal length of day, throughout the entire season, flowered when the photoperiod had reached ten hours and twenty-nine minutes,  - 65 -  .  L and LT did not flower u n t i l they had been exposed f o r two weeks to the same day length as the control group. the  They flowered when  day had become eleven hours, twenty-two minutes. At the time of the termination of the experiment, A p r i l 3,  19*7, a l l plants of the L groupings presented a most remarkable appearance.  Leaves and stems drooped downward, almost p a r a l l e l i n g  the main stems. yet  The. f o l i a g e displayed a pronounced, yellow colour;  no disease was apparent.  The effect d i d not seem traceable  to nitrogen deficiency, for.near the tops of stems, young leaves, which had developed a f t e r the plants had been moved to the h o r t i c u l t u r a l research room, were of a deep healthy green. # Suckers, a r i s i n g from the bases of stems were also healthy. The Comparative E f f e c t s of Pre-Irradiation and Flower Spray of Indolebutyric Acid. 5000 P i P. M. i n Water, on Tomato TfVn**  fi * c  nr.fl  V<»M.-  The treatments here were f o r the f i r s t c l u s t e r s of groups NT, P and PT.  The data are presented i n Table 1 and Table 6.  These show that both treatments were e f f e c t i v e , but indolebutyric a c i d the more so. Treated c l u s t e r s developed uniformly sized bands of f r u i t , as treated flowers tended to develop f r u i t together. not  This was  the case with untreated flowers. Flower buds sprayed at a very early stage sometimes withered  away.  Flower parts persisted where f r u i t had set. Slight epinasty was occasionally noted twenty-four hours  # The damage was due, probably, to the q u a l i t y of a r t i f i c i a l i l l u m i n a t i o n supplied.  - 66 a f t e r the spray had touched f o l i a g e ; but there was a rapid recovery i n a l l cases.  Variety may have been a.factor,as indolebutyric  acid  i s considered as harmless to f o l i a g e . The Comparative E f f e c t s of I r r a d i a t i o n and the  Application.  to Emasculated Flowers, of Hormodin Ho 1 Powder on Tomato F r u i t Set and Yield: Here the second clusters of groups HT, P, PT, L and LT were involved. The data are set f o r t h i n Table 2 . There was a lack of uniformity i n the development of treated flowers into f r u i t y because a l l were not treated at one time. The percentage of parthenocarpic f r u i t was higher than f o r other accid  treatments, because of emasculation.  Pre-irradiation  was  without e f f e c t . The Comparative  E f f e c t s of I r r a d i a t i o n and a Flower Spray of  Indolebutyric Acid. 100 B. P. M. j n Water, oq Tomato F r u i t Sfit and Yield! The treatments, on t h i r d c l u s t e r s , were f o r the groups HT>  P and PT.  The data are presented i n Table J.  Ho seedless f r u i t s were found i n the c l u s t e r s , showing 100 p. p. m. of indolebutyric inducing parthenocarpy.  a c i d to be i n e f f e c t i v e f o r  P r e - i r r a d i a t i o n was without e f f e c t .  The Effect of a Simulated Long Day on F r u i t Setting i n Tomato Plants: Pa, the group, which, during the p r e - i r r a d i a t i o n of the P groupings, was given* by capping, a photoperiod intended to  - 67 simulate that of other P groupings i n t o t a l length hut which a c t u a l l y t o t a l l e d fewer hours of l i g h t , flowered on the same dates as other P groupings.  The y i e l d and degree of f r u i t setting attained  by the Pa group are set f o r t h i n Table  4,  The E f f e c t s of Dilute Concentrations of Indolebutyric Acid Applied i n F o l i a r Sprays to Tomatoes P r i o r to Flowering The data, here are derived from the S group and are set f o r t h i n Table 5.  There was no increase i n f r u i t set.  At no time was v i s i b l e damage of any kind observed on the plants as a result of the f o l i o r sprays i n the concentrations used. Some General Observations From A l l Treatments:By the use of diagrams, kept with the records, i t was possible to follow the h i s t o r y of individual flowers. Sometimes very young flower buds, completely enclosed, and about \ inch i n length, f a i l e d to develop, and withered away following the application of the e f f e c t i v e spray of 5000 p.p.m. of indolebutyric acid.  These l a s t formed buds u s u a l l y f a i l e d to  develop i n unsprayed c l u s t e r s as well, because of the competition for n u t r i e n t s from f r u i t already set. F r u i t development where flowers had been treated with an e f f e c t i v e concentration of the hormone was much more rapid than that of f r u i t set from untreated flowers.  At the f i f t h  day,  diameter s i z e was often two to three times as great. Sometimes treated ovaries developed before the petals of the flowers had opened.  Frequently the set f r u i t burst through  - 68 the side of the f l o r a l envelope. Treated flowers frequently opened following treatment, and f e r t i l i z a t i o n " t o o k place. Occasionally ovaries developed into parthenocarpic f r u i t s when sprayed a f t e r the petals had f a l l e n . The single delayed spray, applied to f i r s t c l u s t e r s , brought about the development of uniformly sized bands of f r u i t s . F r u i t s developed from sprayed blossoms were more d i f f i c u l t to remove from the plant than f r u i t s developed from untreated flowers. Young, sprayed blossoms sometimes developed smaller f r u i t s than opened blossoms, when sprayed with an e f f e c t i v e concentration of the organic a c i d . In general, parthenocarpic f r u i t s were as well-shaped as seeded f r u i t s , excepting i n seven f r u i t s which showed decided proturberances where styles had been stimulated to development at the blossom end.  There were more malformed natural f r u i t s ,  because the f i r s t f r u i t set on an untreated cluster, having, at first,  no competition f o r nutrients, often grew so r a p i d l y as  to become cat-faced i n shape.  This was not found with seedless  fruits. In seedless f r u i t s , pericarpal tissue tended to develop more r a p i d l y than placental t i s s u e s . often displayed hollow locules.  Small,parthenocarpic f r u i t s  However, these seemed to f i l l  with a gelatinous material as f r u i t s matured, f o r older f r u i t s were u s u a l l y well f i l l e d . Seedless f r u i t s were sweeter i n flavour than normal f r u i t s .  Some f r u i t s contained both, seeded locules, and seedless locules. Treated, unopened flower buds tended to develop into parthenocarpic f r u i t s more often than flowers treated when open. There was a l i m i t e d incidence of blossom end rot i n both treated and untreated groups.  - 70 PRESENTATION OP RESULTS FOR THE SECOND YEAR Although, during 194-7, indolehutyric acid, 5000 p.p.m. on f i r s t c l u s t e r s increased f r u i t set over f i r s t c l u s t e r controls 14 per cent more than Hormodin No 1 on second clusters increased set over that i n second c l u s t e r controls, t h i s was not due to a difference i n materials and concentrations,  A study of Tables  I and 2 shows that the difference was due to an increase i n natural f r u i t set on control second c l u s t e r s , which decreased any lead i n set due to the use of hormones.  Thus, as days  lengthened, f r u i t set i n controls improved so that any possible advantage to be derived from the use of growth regulators beoame l e s s i n each succeeding c l u s t e r . when untreated  c l u s t e r s showed as much set as those treated  with indolebutyric acid 100 p.p.m, could have been  Thus, on t h i r d c l u s t e r s ,  i n water, true r e s u l t s  Obscured by the improvement i n natural set, and  not due to the acid being i n e f f e c t i v e . The only r e a l j u s t i f i c a t i o n s for claiming 100 p.p.m. as i n e f f e c t i v e l i e s i n the facts that the natural increase was s l i g h t and that there was no parthenocarpy. Hormodin No 1, applied to ovaries of emasculated second c l u s t e r flowers produced more parthenocarpy  than any other \;  treatment, and was e f f e c t i v e , though natural f r u i t set had g r e a t l y increased. From the f a c t s enumerated above i t appears that i t i s possible to make a true comparison of the e f f e c t s produced by  d i f f e r e n t concentrations only when a l l are applied to the same c l u s t e r of plants at,or near, the same stage of growth. e f f e c t s are most marked on f i r s t ^ c l u s t e r s .  Obviously  Therefore, i n 1947-  1948 the e f f e c t s from spraying f i r s t c l u s t e r s only were considered. This l i m i t e d  i n f l u e n c i n g factors, and made possible a more conclusive  decision as to causes. No epinasty was "noted during the year; and no blossom end r o t . The use of organic acids, where e f f e c t i v e , . r e s u l t e d i n bands of uniformly sized f r u i t s of high q u a l i t y .  Indolebutyric  a c i d used In a 0.02 per cent concentration d i d not s i g n i f i c a n t l y increase f r u i t set over that of controls. A l l other spray applications produced s i g n i f i c a n t increases i n f r u i t set. No effectives)spray proved s i g n i f i c a n t l y b e t t e r than any other.  There  was no s i g n i f i c a n t difference due to time of sowing, the year or the variety.The t o t a l y i e l d s from sprayed c l u s t e r s weije s i g n i f i c a n t l y greater than those from untreated c l u s t e r s due to increased f r u i t set. This year there was no increase i n the average weight of mature f r u i t s due to treatments.  F r u i t s from treated plants  averaged rnine to the pound as d i d f r u i t s from c o n t r o l s . The tables of t e s u l t s f o r 1947-1948 follow Table 6v These show that f r u i t s from treated clusters had t h e i r ripening periods decreased  5 to 7 days. These f r u i t s were, i n general, of good quality  and appearance, excepting that those r e s u l t i n g from treatments of "Fix", and to a lesser extent "Seed-Less-Set", frequently had unsightly protuberances  at t h e i r blossom ends due to a development of s t y l e s .  Parthenocarpic f r u i t s were, again, much sweeter thannnommal ones.  Fruits from Treated and Untreated Tomato Flower Clusters  Fig. 1. A. plant of the Vetomold 121 variety of tomato. The irregularly sized f r u i t s i n the upper cluster developed from untreated flowers. The uniformly sized f r u i t s of the lower cluster developed from flowers treated with indoletratyric acid 500 p.p.m.  Fig. 2. As under figure 1.  Table 1" The Comparative E f f e c t s of Pre-Irradiation and a Flower Spray of Indolebutyric Acid, 5000 P.P.M. i n Water, on Tomato F r u i t Set and Y i e l d Cluster: «J Date of FloweringSFeb. 21, 1947 Treatment: Indolebutyric acid 5 0 0 0 p.p.m. Date Treated:..„„.Feb. 26, ' * 111! Date Harvested: TT A p r i l 3,1947  8)  1 PM  Buds on Cluster Grbb.p### PT N NT •1 16 8 15 7 t 11 8 8 13 2  rH  COm  4  o  8  12-  7  9 5  •H  f  /  £3  o  tJ> EH  77  - 14  7  15  14  5;  8  13  11  37  163  270.1  305.5  371  4  5  ~ 7  13  29  153  247  312 .  440  7 .  7  26  225  290  300.4  449.5  3.11  398.3  302.2  335.1  8. ~ - 7" 5  •': 7r  7  4 -  H  ,4.  7  26  211  281  8  5  7  8  8  28  174  "2415  •14  6  8-  7  13  34  214  a-— -11  14  39  230 '  61  87  260  M  7.  "8'  7  8  08  8  fi  14  6  82  4o;  68^  Total Across 41  Y i e l d __ Immature Fruits Seedless F r u i t s (Grama) _ Group Group NT PT ' N JEJL 111 255 292 401  5  8  6  U  o U  8-  3  Ho. of F r u i t s Set Group N N T PT  ;  72  _  _  Percentage Set -- - 5 8 . 8 95.3 8 7 . 8 94.6 feroeBtftgR Parthenocarpy Ay. W t . p f F r u i t s (Crramn) Ax. # Date of Opening of F i r s t Flower ### Control Group  20  29  Grand_ Total  3?.7fi  ;l 4 8 1 :  -'  263.5  . 513. :  •280 -  311 .4  2128.1  -8*47:5; j  371 •  GraBfl. Total  <  "9117.  33.3?  -34-^0 34^. F i n a l Harvest (Does not r e f e r t o pickings of mature f r u i t s )  I ro I  :35.2  Table 2 . . . T h e Comparative E f f e c t s of I r r a d i a t i o n and Hormodin No. 1 Powder on Tomato F r u i t Set and Y i e l d Cluster .........2 Dates of Flowering March 3,194-7 (N and P Groups); March 7 , 1 9 4 7 ( 1 Groups) Treatment Hormodin No. 1 Powder Date Treated From March 3 and 7 as Flowers Opened Date Harvested .April 3^1947 ~ Yields of Immature F r u i t s as Indicated by Total . . Buds on Cluster No. Fru i t s Set See dies s Diameter Headings i n Cms. Gi oup 1rrou Total Per P Lant , Lcross P PT L LT N N P PT L PT LT N P NT NT LT NT NT PT L >  13  14  8  8  8  7  8  12  9  8  ,4  6  45  16.7  29.5  14. 0  7  7  6  8  8  7  5  7  6  8  5  7  58  10.4  19.3  1 1 .6  9  8  8  7  7  7  7  8  8  7  5>  7  42  14.7  21.5  7  7  13  15  •7  8  7  7  7  13  5  b  47  14.. 6  8  7  8  8  7  7  5  7  8  -'5  7  V7  10 13  8  7  11  10  6  8  8  7  44  8  5.  9  6  8  7  41  11  7  7  8  5  8  5  7  40  6?  61  52  68  50  68  40  .56  1 XD  o  "A C&  r-l  PH  «w  ° xa  °  1 5.4  LT  •Total Across  99.8  9.2  15  22.0  11 . 0  16.0 9 0 . 3  1547  16.2  10.1  17.5 9 5 . 7  19.2  14.3  34.0  11.2  20.C 1 1 3 . 3  10.6  18.6  10.4  18.0  8.8  16.C 8 2 . 4  l6.?9  24.5  10.0  18.1  8.0  18.C 9 5 . 5  10.5  24.0  11  .0  21.3  111.0  14.7  10.9  12.0  18.0  9.1  109.1  167.5 99.0  -Z  >  4  5  .3 < CD  CO 7 : ' 8 Group Total  9 8  9  7  8  9  8  8  8  70 7?  70  70  7  Pei cen* age Fru: t Sei  74^  Pe] cen age Par ;hen tear >y -  Av, Di( met I srs  Cms )  | to- a l : iel< is b; f We Lght (Gr ims) r  6  S3.? 7 t 1 >?-5 91,8 ?  57  334 <  55  -45  163.0  7».4  17.c 9 4 . 8 20.1  I39.e" 7 5 6 . 6 Total  ?7.1 ?7t 1 ?1,8 --  36,4 34,6 3 0 , 4 2.1 270  2.4 307  -••  1.98  294  84.8  2.4  1.8 -  ?2?  12.5  Table 3 . . . T h e Comparative E f f e c t s of I r r a d i a t i o n and a Flower Spray of Indolebutyric Acid, 100 P.P.M. i n Water, on Tomato F r u i t Set and Y i e l d . Cluster:.., 3 Date of -Flowering; March 1 2, 1947 Treatment: Indolebutyric A c i d 100 P.P.M. Date Treated: March 17, 1947 Harvested: A p r i l 3,1947 Buds on Cluster No. o f F r u i t s Set Parthenocarpy Y i e l d Immature F r u i t s (Grams • * 1 Group .i| ITotal NT P i IN NT P PT |i)N NT P PT {Across N NT P PT N 30.1j 25.4" 20.5, 2 2 . d 18 iC8 18 | 8 |!8 16 |5 6 | 25 i ii i ! i ti i t. i ! ! ! ! i i i ii i ii 5 ! 21 21:;q"19.6j 19.Q 18.4| ! 116 !5 15 i 9 i -B - 9 i .i II i j • i i i ! i i i II i i b  3 I-l  o 8  u  CO  ! 8  i i  1  i i  !8  i 111 .  E-i  5  1 37.Cj 24.^ 31.4< 2 0 . q  i 27 i 1  i  *  6  18  1  27  27.2  ' ' i 23.6; 24.0 30.4J  10  8  7  fc  J7  &  7  | 25  20.fi  28.q 2 3 . B 2 6 . 0  5  -i 1 24  j  111  1  8  8  !7  8  67-;  | £ 6 :'  7  '6  no  i i 1 ! j j? M  9  \f>  jIO  i i  i!  J7  1  o +» uo  18  i  8  1  tt  16  "I I  8  8  :8  l!8  ~8  8  S 8  10  C8 9  •• * i-  i i  b  i 1  8  V  }5  1 P i i  ,7  i |5  '  i  i i  J  J  20.3  I  |  J  28.1i  !  I  23.5J 17.7J  i  '  1  18.4 27.6a 3 2 . 8 28.Q  27  ! i 24  1  '  76.1  74.2 73.1  • ii  I I  •  75  0  0; 0  0  Partheno c arp i c Av. F r u i t Wt. (Grams)  1  2 3 . 6 ,20.21 19.8! 3 2 . 4  :  Percentage Set  I  3.9 4.Q3 3.97 3SS2 !  !  f  - 75 -Table 4 . -  ( Figures are averages f o r four plants.) Pa  i Plants. Cluster 1 F r u i t s Set Y i e l d (Grans) (Percentage)  2 Yield  Set  3. Set  Yield  i  86.2  1211  Table 5 . -  67  87.8  (Figures are averages f o r four plants.) .  .5  J Cluster 1 2 F r u i t s Set Yield ( G r a m s ) S e t (Percentage)  61  69  149  737.4  71  3 • YieldSetYield  152  76.4  103  Table 6 . Weights of Mature F r u i t s (Grams) (First cluster) NT  N  1  44  65  2  48  57  3  53  45  4  47  65  5 6  55 61  67  7  48  8 9  50  10 11 12 13  14 15  16 17  18 19 20  50 45 44 51 51 45 52  •  F r u i t s from treated plants Totals 0 . 6 per cent more by weight than f r u i t from the control group,  55 55  48 45 62 55 5©  48 51 50  56 i n d i c a t i n g a 0 . 6 per cent greater average 47 64 54 84 weight at maturity. E. D. i s 2 . 7 which 53 41 f a l l s short of s t a t i s t i c a l significance 45 51 . 63 1044 Mean 5(2.? 1Cv76  Mean 53i*S  Table 7 T h e Comparative E f f e c t s , on Tomato F r u i t Set, of Indolebutyric Acid 3000,500, and 200 P.P.M. i n Water, and the Commercial Preparations " F i x " and "Seed-Less-Set" Cluster 1 Date of Flowering... .February 23,1948 Treatments As Above Date Treated... February 28,1 948 ! as on u. .uster V121A VI2 B C cc C (JrouD b b a c a 8 S e r i a l 1, 8 8 12 8 8 7 9 Hos. 2 8 8 8 8 8 11 8 7  Group Total  01  VI2  C 7  AC b a 8 8  c 7  8  8  8  C  C  JJTU I T S  71 2 IB ft b 6 8  6  8  b 8  8  4  8  8  8  4  8  8  4  : ' ' Total A Cross  DCu  6  4  a 8  8  7  4  AC!  b 6  :c 6  78  7  6  5  77  8  8  4  72  3  8  10  8  8  9  8  8  7  8  8  8  8  0  8  8  4  5  8  6  7  4  12  7  8  8  8  8  8  12  8  8  8  7  8  6  8  4  3  8  8  10  4  7  8  4  78.,  5  8  8  8  10  8  8  8  7  8  7  7  8  5  7  8  4  6  8  8  6  3  6  7  5  —o% 73'  6  8  8  8  12  8  8  8  12  10  7  8  7.  8  8  7  5  8  8  8  8'  5  7  8  6  86  5J  49  49  54  53  48  53  49  46  47  31  45  47  33  46  46  43  43  611  90/ 95* 83.4J53  Percentage Fru i t S et  45  91 A 95.5  A difference between group t o t a l s greater than 9.8 indicates a s i g n i f i c a n t difference.  44  30 164  ?0.3 66i brand total  - 77 Table 8  WEIGHTS OF MATURE FRUITS FROM FIRST CLUSTER TOMATOES GROW DURING THE SECOND YEAR F r u i t s were picked as each became ripe. Though  most f r u i t s from  treated clusters maturecL i n s i z e , c l o s e l y together there was some spread i n t h e i r ripening periods; but t h i s , although up to s i x days, was not so great as f o r f r u i t s from.untreated clusters, where the spread  # was Up to two weeks. For marketing purposes i t should be possible to pick a treated c l u s t e r at one time, f o r when the f i r s t ripened f r u i t s have become red the l a t e r ripening f r u i t s are usually of a s a t i s f a c t o r y oraage^plnk.. Total crops were taken f o r a l l controls and groups treated with indolebutyric acid-500 p.p.m.,and crops from two plants, having 8 and 6 f r u i t s , f o r a l l other treatments excepting indolebutyric a c i d 200 p.p.m., where no harvesting was done. Date of Ripening of F i r s t F r u i t Anril 14 21 15 V121A Group C a b No. of 6 Plants 2 6 Total 1525.2 716.8 2458.1 Wt.. Grams No. of 14 Fruits 31 47 Average 49.2 Wts., Grams 51.2 52.3  16  1?  c  22 AC C  a  b  2  6  2  6  24 V121B C  19  19  17-  a  b  6  2  6  1533  754.6  2212.6 684.6  1 2 1 8 . 4 672..  2i;i  *  30  14  46  14  26  14  43  51;.1  53.9  48.1  48.9  48.4  48  49  F i r s t f r u i t s ripened on treated clusters f i v e to seven days e a r l i e r than on controls. The data above show increases i n weight on c e r t a i n treated clusters to be nearly the same as the previous year. Furthermore, there i s not always an increase. There are no s i g n i f i c a n t differences(betweenthe ^weights o f mature f r u i t s duetbbarmine treatments.  # U n t i l M&y 6/1948.  - 78 DISCUSSION OP RESULTS The r e s u l t s obtained i n the present experiment may considered from two avenues of approach.  be  In the f i r s t place,  there are those effects which have been observed d i r e c t l y , and may be interpreted by inspection.  Secondly, there i s some mass  d e t a i l which must be analyzed, with the a i d of mathematics, before a true p i c t u r e , of what a c t u a l l y has happened, may be presented. In the following pages an attempt has been made to separate observed d e t a i l into l o g i c a l parts. THE FIRST YEAR" The E f f e c t of an Excess n f FVunreflcent Light on the :  I n i t i a t i o n of Flowering i n the Tomato Plant The L and LT groups started to flower under a f i f t e e n hour photoperiod.  Above f i f t e e n hours and thirty.minutes flower bud  formation ceased.  These plants were placed under normal day  conditions on February 21, and flowered on the same day as the La and Pb groups, which was a f t e r the photoperiod had r i s e n beyond i t s length on February 21. The flower buds already formed on the L and LT plants persisted under the normal day, but d i d not open. An e f f e c t i v e photoperiod and l i g h t source does not immediately i n i t i a t e flowering.  The plant must be subjected to  i t f o r at l e a s t two weeks. I t would appear., that an excess of illumination of the q u a l i t y f)  provided by the  typ© of fluorescent lamp^used causes v i s i b l e changes  -7?." i n the f o l i a g e of tomato plants; and that these changes may properly be regarded as Injury.  I n h i b i t i o n of flowering may  be due to the same cause. The Comparative E f f e c t s o f Pre-Irradiation, a Flower Spray of Indolebutyric Acid. 5000 P. P. M.. i n Water, a Flower Spray o f Indolebutyric Acid. 100 P. P. M.. and Hormodin Ho 1 Powder. A P P l i e f l to th? PYMTlSg Pf ^ g c i a l f t l f e a Flowers; The data from Tables 1, . 2 , and 3 , regarding f r u i t set, were taken together and subjeoted to an analysts o f variance, the c a l c u l a t i o n s o f which are on page 8 6  . A s i g n i f i c a n t difference  between group t o t a l s , f o r P- 0.05# was found to be 1 5 . 3 1 6 $ and a s i g n i f i c a n t difference between group means to be 1 . 8 6 4 . On the basis of group means;; i t was found that indolebutyric acid, 5000 p.p.m., applied as a water spray, and Hormodin Ho. 1 powder, i n a l l cases s i g n i f i c a n t l y increased f r u i t set beyond that of controls and i r r a d i a t e d groups excepting i n the case o f the  first  c l u s t e r s o f P group, which set a s i g n i f i c a n t l y greater quantity of f r u i t than f i r s t c l u s t e r controls, but d i d not maintain the lead on succeeding c l u s t e r s .  Thus, a r t i f i c i a l  i r r a d i a t i o n of tomato seedlings  four hours d a i l y for a period of twenty-two days while the plants were i n the f l a t stage, s i g n i f i c a n t l y increased f r u i t set on the f i r s t c l u s t e r s , and t h i s was further increased by a combined a p p l i c a t i o n o f indolebutyric acid, 5000 p.p.m. i n water and p r e - i r r a d i a t i o n , making the two together treatment f o r the f i r s t c l u s t e r s . P seemed a f a c t o r .  s i g n i f i c a n t l y the best  I n i t i a l l y heavy flowering on  - 8o Indolebutyric a c i d |000 p.p.m. and Hormodin Bo.  1 powder,  showed no s i g n i f i c a n t difference between t h e i r e f f e c t s .  The spray  caused temporary damage to f o l i a g e . Indolebutyric a c i d 100 p.p.m. set l e s s f r u i t than controls; and there was no evidence of parthenocarpy. was  The concentration  completely i n e f f e c t i v e . There was a large increase of f r u i t set on., the second  olusters o f controls . k further increase on t h i r d c l u s t e r s was much less. Y i e l d by weight, at an immature stage for the f i r s t c l u s t e r * i s analyzed on page 8>P . Indolebutyric a c i d , 5000 p.p.m., and p r e - i r r a d i a t i o n were found t o s i g n i f i c a n t l y increase y i e l d s o f immature f r u i t s due to increased set and an even and r a p i d rate of growth.  In the case of  pre-irradiation, i n i t i a l l y heavy flowering was a f a c t o r .  The r e s u l t s  showed more but smaller f r u i t s , except at maturity (Table 6), when f r u i t s from treated flowers were larger i n d i v i d u a l l y , but not s i g n i f i o a n t l y so. Y i e l d s , as indicated by f r u i t diameters at an immature stage of c l u s t e r 2, are analyzed on page was  86  • Hormodin Powder No. 1  found to s i g n i f i c a n t l y increase the y i e l d of immature f r u i t  from treated plants, over that from untreated plants. was  The increase  due to greater set and a more even, and rapid rate of growth. Table 3 shows that there was no s i g n i f i c a n t difference i n  immature y i e l d s due to the use o f indolebutyric a c i d 100 p.p.m., which was completely i n e f f e c t i v e .  I t was found that Hormodin No. 1 Powder increased the percentage of parthenocarpic' f r u i t 26 to 37 per cent over the numbers of seedless fruits found as a r e s u l t of the use of indolebutyric acid 5000 p.p.m. This may be explained by the f a c t that flowers were emasculated p r i o r to the application of the powder, and there was, _ therefore, no further opportunity f o r p o l l i n a t i o n to take place; whereas p o l l i n a t i o n frequently took place a f t e r the use of the spray, the f l o r a l parts not being removed. The Effect of a Simulated Long Day on F r u i t Setting i n Tomato Plants!,* By capping the growing t i p s of the main stems of tomato plants, so that the t i p s are subjected to alternating periods of l i g h t and. darkness, not exceeding s i x hours, a day-length may  be  simulated which corresponds i n i t s effect to a long day, though l e s s photosynthesis has taken place. The Pa group flowered at the same times as other members of the ,E. ,? groups.and set f r u i t , and gave y i e l d s , i n numbers and quantities, p a r a l l e l i n g the P group.  This i s shown when Table 4 i s  compared with Tables 1, 2 and 3 , Pa received l e s s l i g h t than P i n the seedling stage.  The  group, therefore, must have manufactured l e s s carbohydrates. ' I f stored carbohydrates, formed during i n i t i a l i r r a d i a t i o n , influence f r u i t set l a t e r on, group P should have set more f r u i t fchan group Pa.  This was not the case;  The only l o g i c a l deduction i s that photoperiod,  simulated  -82or normal, i a the i n f l u e n c i n g f a c t o r i n f r u i t set, and food relationships within the plant. The E f f e c t s of D i l u t e Concentrations  of Indolebutyric Acid  Applied i n F o l i a r Sprays to Tomato Plants P r i o r to Flowering; There were no v i s i b l e e f f e c t s from the a p p l i c a t i o n of these sprays.  Table 5 shows that f r u i t set, and y i e l d c l o s e l y  p a r a l l e l e d those of the control group.  The sprays appear to  have been completely i n e f f e c t i v e . THE SECOND YEAH Hormone treatments were applied to the flowers of f i r s t c l u s t e r s only, because these c l u s t e r s are the ones which i n v a r i a b l y 2  show the poorest f r u i t set under winter conditions. remain vegetative and never open into flowers. f a i l to set f r u i t .  Many buds  Open flowers  often  Young f r u i t s sometimes drop.  Of the chemicals used, only indolebutyric acid, 200 p.p.m. i n water f a i l e d to increase f r u i t set s i g n i f i c a n t l y ; but c l u s t e r s treated with t h i s concentration d i d show a s l i g h t increase, p a r t i c u l a r l y on A i l s a Craig, the poorer setter, a l l other sprays increased f r u i t set s i g n i f i c a n t l y from  t o ^ l ^ p e r cent.  No one of these e f f e c t i v e sprays was s i g n i f i c a n t l y better than any other,, although the proportionate increase on A i l s a Craig was, i n a l l cases , somewhat higher, because i t s natural set i s lower than f o r Vetomold 121, which seems to be a better greenhouse variety. From the tables for both years i t may be seen # See pp. 7 0 and 7 1 .  that  -83indolebutyric acid  5000 p.p.m. and 3000 p.p.m. were no more e f f e c t i v e  than the acid used i n a concentration of 500p.p.m. As the increased sets t h i s year were not s i g n i f i c a n t l y d i f f e r e n t from those produced hy indolebutyric  5000 p.p.m. during  1946-1947* there appeared to be no effect due to the year. Though not a l l sown at one time , a l l plants flowered February 23, 1948. differ.  Yields and increases i n set d i d not g r e a t l y  Thus the time of sowing and season were without e f f e c t . In t h i s experiment v a r i e t y d i d not prove to be an. important  factor, although vetomold 121 set more f r u i t n a t u r a l l y than A i l s a Craig.  After hormone treatments t o t a l sets were nearly the same. There was no s i g n i f i c a n t increase i n the average size of  mature f r u i t s due to the use of hormones. Measured by the t o t a l weights and.the t o t a l numbers of f r u i t s , e f f e c t i v e hormones d i d increase y i e l d s s i g n i f i c a n t l y . The use of e f f e c t i v e organic acid sprays resulted i n bands of uniformly sized f r u i t s , f o r an even growth was stimulated even when natural p o l l i n a t i o n had already been e f f e c t i v e .  F r u i t s were often  of b e t t e r quality and flavour. No e f f o r t was made in. 1948 to determine the numbers of seedless f r u i t s ; but c e r t a i n other general observations were made. Hormones seemed to decrease the ripening period by 5 to 7 days. Sprayed f r u i t s d i d not drop; and i t was more d i f f i c u l t to remove them from the vines. Sprayed f r u i t s , i n general, displayed a persistence of  - 84 perianth up to ten days. Protuberances at blossom ends, due to an over stimulation of styles, made "Fix" a less valuable material than the Others used. "Fix" resulted, also, i n a greater proportion of hollow locules. With indolebutyric acid spray seedless locules were usually f i l l e d , at maturity, with an edible, gelatinous material. The sweeter flavour of parthenocarpic f r u i t s has been found to be due, mainly, to a s l i g h t , but not significant, increase i n sugar content. There i s , also, a non-significant decrease i n ascorbic acid content below the normal for any season or variety; and a lowered pH may accentuate a sweetness of flavour. However, seedless tomatoes are high i n food value as seeded ones (17), and seeded f r u i t s developed from hormone treated flowers d i f f e r l i t t l e from normally produced seeded f r u i t s .  -85-  Analysis of Variance of F r u i t Set of Tomatoes f o r Three Clusters Based on Tables 1, 2 and 3 . Cluster N Group 5 5  4  1  NT  7 '8 5  7 4 11 5 •7 6 8 6 8 5  15 13  7 7 4 8 7 11  40  61  5  7.6 9  Totals  72  .2.  N  PT  P  NT  2  3  PT  L  7 8 5 5 7 6 8 4 7 8 8 7 5 7 7 7 13 5 8 5 7 5 5 8 10 6 8 5 9 6 8 6 5 8 5 8 5 7 68 50 68 40 52  14 11  8  13  •7 7 8 13  14 87  12  10.9 6.5 ,2 .  Total S.S i s 5 + 5  P  o .  t  + + 7  6.,2 6. .5  8.5 „  2  _ . 2  + 8 *- J2A~  N  LT  6 7 7 8 7 7 7 7  NT  8 6 6 5 8 6 7 6 5 7 6 7 5 7 6 5 51 49  56  P 5 5  PT  6  Totals  5 5  8 6 8 6 7 6 5 8 7 5 8 51 49  113  97  103  102 90 94 102 102 794  6.4 6.2 6.,4 6.2  5 7  620.1  112 Between group S.S. i s 40 4- + 4 9 - 7 9 4 2  2  8  Within group  279.35  S.S. i s 6 2 0 . 1 - 2 7 9 . 3 5 -  Factor Total  S.S Peg. Freedom 620.1 111  Treatment  279.35 340.75  Error  2  112  13 98  Variance C 21.488 3.477  3*0.15 F. 6.18  nl i s 1 3 , n2 i s 9 8 F from the table of F for ns  12 and 100 and P 0.01 i s less than 2 . 3 6 P 0 . 0 5 i s less than 1.85 proving group variance s i g n i f i c a n t l y greater than that f o r error.  J  A difference between group t o t a l s greater than 3 . 4 7 7 times 8 times 2 times 2 ( P 0 . 0 5 from table of x because Deg. Freedom Error are greater than 30) equals 7.45 times 2 equals 14.9 i s s i g n i f i c a n t A difference between means greater t h a n V 3 . 4 7 7 t i m e s 2 times 2 equals .932 times 2 8 equals 1 . 8 6 4 i s s i g n i f i c a n t These f i g u r s show a l l chemically treated groups, excepting those treated with indolebutyrio acid 100 p.p.m., to have set s i g n i f i c a n t l y greater quantities of f r u i t s than a l l other, groups excepting P, the pre-irradiated group, PT i s s i g n i f i c a n t over a l l groups.  -86-  Analysis of Variance of Yields by Weight for the First Clusters of Tomatoes as Affected by Pre-irradiation and Applications of Indolebutyric Acid 5000.P. P. M. to Flowers The arrangement of plants was purely random. Yields were measured in grams, and are given in Table 1 for cluster 1 for each plant in each group. Weights are for immature fruits. Total S.S. is  111  + + 295  Group S.S. is 1481 -  2  f»  2  -  9  117.5* P  3060.9^  3  , 195761.68 or  2  - C. F., or  Error S. S. is the- above two subtracted, or Factor  -S.S.  23344.97  Peg- Freedom  Total  195761.68  31  Group  172416.71  3  Error  23344.97  Varience  -  _F. -  57472.23 68.9  times  8  times  833.88  28  The reading of F is significant. difference between totals for P 0..O5 is ^833.88  172416.71  8  2  times  2,  or  115  A significant  times  2,  or  250  Thus m is significant over 1, P over NT, and PT highly significant over a l l . Similarly total yields for second cluster fruits at an immature stage show Hormodin No. 1 as causing significant increases. In this case yields were.indicated by diameter readings of fruits. When data were analyzed, as above, a. significant difference between totals was found to be  29.84  for P  0.05.  ANALYSIS OF VARIANCE OF FRUIT SET OF TOMATOES CROWN THE SECOND YEAR Data from Table 7 Total S.S. i s 6 + + 6 _ 4641 2  2  =  2 2 2 Between group S.S. i s 31 4- 4- 30 464 6 72 Within group group S.S. i s 233.8_114.1 = 7  Factor  S.S.  Total  233.8  71  Treatment114.1  11  2  Peg. Freedom  114.1 119.7  Varianee  F.  10.37 5.1 9 l  Error  119.7  ii] i s 11J n  2  60  2.00  i s 98  F from table of F for the above i s : f o r P  0 . 0 1 , 2.56  for P  0.05, 1.95  proving group  variance s i g n i f i c a n t l y greater than that f o r error. A difference between t o t a l s greater than  2 times 6 times 2  times 2 — 9 , 8  i s significant for P 0.05 Thus, a l l treatments but indolebutyric acid 200 p.p.m. were s i g n i f i c a n t over controls. None of these e f f e c t i v e s were s i g n i f i c a n t over another. In a l l cases the increases on A i l s a Craig were somewhat greater than on Vetomold, but not s i g n i f i c a n t l y so. A i l s a Craig appears to produce fewer flower buds and set l e s s f r u i t n a t u r a l l y than Vetomold 121. There were minor increases i n f r u i t set where indolebutyric acid 200 p.p.m. was used; but these f e l l f a r short of significance. These increases were s l i g h t l y greater i n the case of A i l s a Craig.  -88SUMMAEY The present i n v e s t i g a t i o n was conducted under the d i r e c t i o n of the Department of Horticulture of the U n i v e r s i t y of B r i t i s h Columbia" during the period Octob.er JO, 194-6 to May 1948.  6  The purpose was to study the effects of l i g h t and applications  of organic acids on tomato plants of the mould r e s i s t a n t v a r i e t y Vetomold 121, and on the variety A i l s a Craig. During the f i r s t year <•fiffty-s'six plants of Vetomold 121, grown i n 10 inch pots, were used i n the experiment; and eight,  were  set aside, under normal conditions, as a control group. Photoperiodic  e f f e c t s were studied by subjecting plants to  I r r a d i a t i o n from fluorescent lamps.  Group P were i r r a d i a t e d i n the  seedling stage for periods of four hours d a i l y f o r twenty-two days.  Group L received up to sixteen hours twenty-nine minutes  of l i g h t d a i l y u n t i l February 21, 1947. Certain members of a l l groups received flower treatments of indolebutyric acid 5000 p.p.m., and 100 p.p.m. i n water  sprays.  Others received treatments of .a commercial preparation of indolebutyric acid i n t a l c , Hormodin Powder ETo. 1, applied to the ovaries of emasculated flowers. F o l i a r sprays of indolebutyric aoid 50, 100, 250, and 500 p.p.m. i n water were applied, p r i o r to flowering, to an S group of plants and produced no e f f e c t s . Excess fluorescent l i g h t was found to i n h i b i t flowering, and  -89to cause p h y s i o l o g i c a l changes of an i n j u r i o u s nature. Ho flowers opened u n t i l the day-length was ten hours twenty-nine minutes. Indolebutyric aoid 100 p.p.m, was without e f f e o t .  As a  r e s u l t o f the spray of indolebutyric j M c i d 5000 p.p.m. the percentage of buds s e t t i n g f r u i t on f i r s t c l u s t e r s was increased ^J3. per cent (Table l ) beyond that of controls. about an increase of 29.0 per cent.  Seedling i r r a d i a t i o n brought Hormodin Ho,  1 increased f r u i t  setting on the second c l u s t e r by 22.8 per cent (Table 2). Set percentages were based on the proportion of f r u i t set to the number of buds formed; and, did not indicate the number of buds formed i n the f i r s t place or the t o t a l number of f r u i t s set i n a group.  In PT,  which received a combined treatment o f p r e - i r r a d i a t i o n and indolebutyric a c i d 5000 p.p.m., t o t a l set was s i g n i f i c a n t over that f o r a l l other groups. Indolebutyric a c i d , 5000 p.p.m., used alone, increased the t o t a l y i e l d s of f r u i t , harvested at an immature stage, 50 per cent by weight.  Hormodin, as a sole treatment, increased t o t a l y i e l d s  53 per cent by weight.  These tremendous increases were due to an  increased set and more rapid growth than normal.  The percentage increase  became l e s s as f r u i t s on untreated plants matured, Indolebutyric a c i d , 5000 p,p,m,, appeared to be responsible f o r an increase of 6 per cent i n average f r u i t weight of mature f r u i t s taken from treated plants. s i g n i f i c a n t difference.  This percentage d i d not involve  a  -90During the second year of the experiment, 1947-194-8, seventy-two plants were used.  Twenty-four of these were Vetomold  121 sown October 27, 1947, twenty-four were Vetomold 121 sown November 12, 1947, and twenty-four were A i l s a Craig'sown November 12, 1947. Each of these three groups was divided into subgroups of six plants, one subgroup being kept as controls.  The remaining  subgroups received delayed flower sprays, on f i r s t clusters onlyi of water solutions of indolebutyric acid JOOO p.p.m., 500 p.p.m.,and 200 p.p.m. and two commercial preparations " F i x " and ^Seed-Less-Set". Indolebutyric acid 200 p.p.m., i n a water solution, f a i l e d to influence set s i g n i f i c a n t l y .  A l l other treatments increased set  S i g n i f i c a n t l y over that on controls. No one solution was s i g n i f i c a n t l y better than any other. In a l l cases f r u i t s from treated clusters developed as uniformly sized hands and were of good quality, excepting that commercial preparations, p a r t i c u l a r l y "Fix", frequently produced unsightly blossom end  protab.ejrances.  Parthenocarpic f r u i t s were  sweeter than normal f r u i t s . There was no s i g n i f i c a n t difference due to time of sowing, the year, or the variety.  Hormones decreased the ripening period 5  to 7 days; and prevented f r u i t drop.  They d i d not increase f r u i t s  size at maturity. Indolebutyric acid was the e f f e c t i v e producing the best quality f r u i t . second year.  About one gram of indolebutyric acid was used the The cost of the a c i d to experimenters averages f i v e  _ 91  -  dollars per gram. Costs may be greatly decreased when the material is supplied for commercial purposes. Because i t was the least concentration of the chemical significantly increasing fruit .set, 5 0 0 p.p.m. of indolebutyric acid».dissolved in v/ater, and applied with a nasal atomizer, appeared to be the most satisfactory spray for increasing fruit set on greenhouse tomato plants.  CONCLUSIONS Prom the data tabulated following observations, and from statistical analyses of these, the following conclusions, valid for the Vetomold 121 and AilsaCraig varieties of tomato, have been deduced: (1)  The initiation of flowering in tomatoes is governed by the  length of the photoperiod; and is not influenced by food relationships within the plant. For the initiation of flowering a simulated photoperiod.seems as effective as a normal one. Vetomold 121 must be subjected to-an effective photoperiod for two weeks before flowering will be initiated.  The effective  photoperiodic range for the initiation of flowering in the varieties has a lover (2)  limit of ten hours thirty minutes.  Excess fluorescent light inhibits flowering in Vetomold 121;  and causes visible physiological changes in foliage which may be regarded as damage. (?)  Foliar sprays of indolebutyric acid in water, 5 0 , 100, 2 5 0 ,  and 500 p.p.m., applied prior to flowering, to Vetomold 121, have no effedt whatsoever. Indolebutyric acid 100 p.p.m. and 200 p.p.m. in water are ineffective in influencing fruit set when applied to the flowers ofn the tomato varieties tested. (4)  Pre-irradiation of seedlings of Vetomold 121 for four  hqurs daily for twenty-two days, following the greening of the cotyledons, results in a significant increase in set and total yield  -93-  for first clusters only. A combination of this treatment and a water spray, on flowers, of indolebutyric acid, in an effective concentration, is significantly more effective in inducing the desired results, on first clusters, than is any other treatment used. "Fix", "Seed-Less-Set", and indolebutyric acid 3000  5000  p.p.m.,  p.p.m., and 5 0 0 p.p.m./applied in water, and Hormodin No.  1  in talc, significantly improved fruit set and yields for the tomato varieties Vetomold 121 and Ailsa Craig; but the first cluster shows the greatest increases. With regard to increased set no one of these hormone treatments is significantly better than any other; but indolebutyric acid produces the best quality fruits. "Seed-Less-Set"  "Fix" and  cause unsightly blossom end protuberances. Under  ordinary conditions none causes plant injury.  There is no significant  difference due to variety, season,or year. Organic acids are most conveniently applied in water solutions.  They are most effective  when applied to flowers as a delayed spray. (5)  All parthenocarpic fruits produced are sweeter than normal  fruits. (6)  Applications of effective concentrations of indolebutyric  acid in water to the flowers of tomatoes results in the production of bands of uniformly sized fruits of good quality maturing at nearly the same time. These fruits mature and ripen 5 to 7 days earlier than fruits on untreated plants. The development of ehscession layers is retarded and, therefore, there is no fruit drop. Even where increased fruit set and total yields are not  required i t seems advisable, in view of the advantages referred to above, to apply water sprays of hormones in effective concentrations to all clusters of greenhouse tomatoes. With commercial crops the use of such sprays should prove profitable. Of the materials and concentrations tested during the present investigation, indolebutyric acid 5<5@.p.p.m. in water, applied as a delayed spray to floral parts, appears the most valuable.  - 95 BIBLIOGRAPHY 1  H i l l , J . B., L. 0. Overholtz, and H. W. Popp. Botany. McGraw H i l l Co., New York,  1:89.  1936.  la  1:86.  1936.  lb  1:88.  1936.  1c  1:92.  1936.  1d  1:92.  1936.  1e  1:86.  1936.  If  1:292.  1936.  1g  1:212.  1936.  1h  1:227.  1936.  2  Auchter, E. C., and H. B. Khapp. Orchard and Small F r u i t Culture. Wiley and Sons, New York. 3:201.  3  1937.  Withrow, A l i c e P., Purdue University Agr. Exp. Sta., Lafayette, Ind. Comparative E f f e c t s of Radiation and Indolebutyric Acid Emulsion on Tomato F r u i t Production.  Proceedings of the  American Society f o r H o r t i c u l t u r a l Science. 4  46:329*.  Howlett, F. S., Ohio Agr. Exp. Sta., Wooster, Ohio.  1945.  The E f f e c t  of Carbohydrate and Nitrogen Deficiency Upon Microsporogenesis and the Development of the Male Gametophyte i n the Tomato. M i l l . Ann. Bot. 50:767-803. 5  1936.  Stoutemyer, V. T., and. F. L. OJRourke, U. S. D. A., Glenn Dale, Md. Booting of Cuttings from Plants Sprayed With Growth Regulating Substances.  6  P. A. S. H. S. Vol. 46.  1945.  Magnus, J . R., L. P; Bayer, and W. C. Baynes, U. S. D. A., B e l t s v i l l e , Md. Attempts to Influence Flower-Bud I n i t i a t i o n i n Apple Trees by Chemical GrowthSSubstances.  P. A. S. H. S. 7  43:51-53.  15*3.  MacDougall, M. S., and R. Hegner. Biology, the Science of L i f e . McGraw-Hill Book Co., New York. 1:355  8  and 676.  Hammer,M. E., Chicago. E f f e c t of Phenylacetic Acid and Naphthalene Acetamide on Tomato Plants Grown i n S o i l . 103 ( 3 ) :  9  Hormones.  576-580.  B i o l o g i c a l Abstracts. Vol. f o r 1928. Paper 9857. and 2 6 , 9 3 3 .  Pesek, Arthur. Wuchsstoffe und Tropismen. 78 ( 2 ) ; 168-186,  Zeitschr. 11  Bot. Gaz.  1942.  Vol. f o r 1930. Papers 5701; 26,931 10  1943.  Oesterreich. Bot. - c  :  ',929.  Gustafson, F e l i x G. Inducement of F r u i t Set by Growth Promoting Chemicals. U. S. A.  Proceedings of the National Academy of Science, 22 (11)  11a Gustafson, F e l i x G.  : 682-636.  1936.  Parthenocarpic and Normal F r u i t s Compared  as to Percentage of Setting and as to Size. Bot. Gaz. 102 (21) 12  Herbst, H.  : 280-286.  1940.  Wuchstoffe i n der gartnerischen Praxis I. Heteroauxin  i n der Tomatenkultur Gartenbauwess. 13  12 (415):5^0-52%. 1939.  Howlett, F. S., Ohio, Agr. Exp. Sta., Wooster, Ohio. An Experiment Concerning the P r a c t i c a b i l i t y of Certain Chemicals as a Means of Inducing F r u i t Setting i n the Tomato Plant. P. A. S. H. S. 3 7 : 8 8 6 - 8 9 0 .  13a Howlett, F. S., Ohio Agr. Exp. Sta.,  1940.  Wooster, Ohio.  The Use of  Chemicals to Stimulate Fruitfulness i n Tomatoes.  Rept.  Vegetable Growers Association of America. 203-214. 13b Howlett, F. S., Ohio Agr. Exp. Sta., Wooster, Ohio.  1941.  Fruit Set  and Development from Pollinated Tomato Flowers Treated with  Indolebutyric Acid. P. A. S. H. S. 41:277-281.  1942.  13c Howlett, P. S., Ohio Agr. Exp. Sta., Wooster, Ohio. Growth Promoting Chemicals Improve Greenhouse Tomato Production. Ohio Agr. Sta. B u l l . 28 (220)  :  17-27.  1943.  13d Howlett, P. S., Ohio Agr. Exp. Sta., Wooster, Ohio. Proc. Am. Ohio leg. and Potato Growers Association.  Mat,  1945.  I3e Howlett, P. S., and R. B. Withrow; Ohio Agr. Exp. Sta., Wooster, Ohio; and Purdue University, Lafayette Indiana. Physiology.  131-139.  1946.  13f Howlett, P. S., Agr. Exp. Sta., Wooster Ohio. Journal. 14  Plant  75 (3) : 9, 4 3 , 47, 48.  Market Growers  1946.  Swarbricke, T., Long Ashton Eesearch Station.  The Effects of  Naphthaleneacetic Acid and Naphthoxyacetie Acid on Fruit Set and Development of Tomato and Strawberry Plants. Long Ashton Ees. Sta. 1942:24-28£ 15  Bretz, T. W.  1943.  INjury to Greenhouse Tomatoes from Volatized Growth  Promoting Substances. 16  Zimmerman, P. W.,  Dis. Reporter. 28 (6) : 2 0 6 .  Present Status of Plant Hormones.  I n d u s t r i a l and Chemical Engineer. Ed. 16a Zimmerman, P. W.,  1944.  Boyce Thompson I n s t i t u t e f o r Plant Research,  Yonkers, New York.  and A. 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Response of Some Garden Plants to the Daily Period of Light. J. Roy. Hort. Soc,  57:321-325.  24 Brown. American Garden Book. Scribners. 753. 25 Meyer, B. S., and D. B. Anderson, Plant Physiology. D. Van Nostrand Co., New York.  1:555. 1946.  

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