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Handling of pears with special reference to the effect of bruising injury upon rate of ripening, respiration… Fisher, Donald Vince 1935

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TEE HANDLING OP PEARS WITH SPECIAL REFERENCE TO THE EFFECT OF BRUISING INJURY UPON RATE OF RIPENING, RESPIRATION AND SUGAR CHANGES. by Donald. Vince F i s h e r A Thesis Submitted f o r the Degree of MASTER OF SCIENCE IN AGRICULTURE In the Department of HORTICULTURE THE UNIVERSITY OF BRITISH COLUMBIA December 1935 TABLE Off CONTENTS Page Intro duct ion I Purpose of Work 1 Review of L i t e r a t u r e 2 M a t e r i a l s and Methods 12 F r u i t U s e d.. 12 Storage F a c i l i t i e s 13 Experimental Equipment 13 Plan of Experiments .......... 14 Experimental Methods ..................... l 6 E f f e c t of B r u i s i n g on Carton Dioxide ..... R e s p i r a t i o n at Room Temperature 22 R e s p i r a t i o n at Room Temperature Under Conditions of Good Aeration. 26 Comparative Rate of R e s p i r a t i o n at Room Temperature f o r D i f f e r e n t V a r i e t i e s 29 E f f e c t of Carbon Dioxide Accumulation upon Depression of R e s p i r a t i o n 31 Rate of R e s p i r a t i o n at 0°C. f o r D i f f e r e n t V a r i e t i e s 32 E f f e c t of Change of Temperature Upon Respiratory A c t i v i t y 3° Sugar Changes During Storage and Ripening. 41 E f f e c t of B r u i s i n g on Sugar Changes and Loss of Weight 45 M i c r o s c o p i c a l Examination of Bruised Tissue 48 Softening of F r u i t During Storage.......... 49 Pressure Test of Experimental F r u i t at End of Storage Period $0 Appearance of the F r u i t at the End of the Experiments Loss of If/eight of Pears during Progress of the Experiments. Discussion and Conclusions.................. Summary L i t e r a t u r e C i t e d . Acknowledgments I TUB HANDLING OJT PEARS WITH SPECIAL REFERENCE TO THE EPPECT OP BRUISING INJURY UPON RATE OP RIPENINGRESPIRATION AND .. SUGAR CHANGES. INTRODUCTION The s u c c e s s f u l handling of any kind of f r u i t from the time i t leaves the t r e e u n t i l i t reaches the consumer i s a d i f f i c u l t problem, i n v o l v i n g many f a c t o r s . This i s p a r t i c u l a r l y true of pears, which have very s p e c i f i c r e q u i r e -ments as to p i c k i n g maturity, length of storage and r i p e n i n g temperature. Given favorable treatment, however, pears show le s s u n i f o r m i t y i n t h e i r response than almost any other k i n d of f r u i t . I t i s a constant source of s u r p r i s e to discover c e r t a i n l e t s of f r u i t r i p e n i n g with, s u p e r l a t i v e f l a v o r , while other apparently s i m i l a r l o t s develop only medium q u a l i t y . Much study has been d i r e c t e d toward s o l v i n g the harvest i n g , storage and marketing problems of pears, w i t h a considerable degree of success. Many of the fundamental p h y s i o l o g i c a l processes underlying s u c c e s s f u l handling, how-ever, are but l i t t l e understood. Since the pear i s a l i v i n g organism, responding to and ca r r y i n g on chemical processes, greater extension of p r a c t i c a l knowledge must invoIve a more complete understanding of the chemical l i f e processes of the f r u i t . Probably the most accurate s i n g l e means of measuring response to d i f f e r e n t s t i m u l i i s by means of r e s p i r a t i o n measurements. In the hope of b u i l d i n g up f u r t h e r knowledge II i n t h i s d i r e c t i o n , t h e work r e p o r t e d u p o n i n t h i s t h e s i s was u n d e r t a k e n . 1. PURPOSE OF WORK The main purpose of t h i s i n v e s t i g a t i o n was to deter-mine whether or not b r u i s i n g i n j u r y to pears, under d i f f e r e n t temperature co n d i t i o n s , influences t h e i r p o s s i b l e storage l i f e as i n d i c a t e d by rat e of r e s p i r a t i o n . The p r a c t i c a l s i g n i f i c a n c e of such information i s obvious, since pears undergo a great deal of b r u i s i n g from the time they leave the t r e e u n t i l they are f i n a l l y consumed. I f , apart from im p a i r i n g t h e i r outward a t t r a c t i v e n e s s , b r u i s i n g also a f f e c t s t h e i r r a t e of r i p e n i n g , i t i s important to know how much r i p e n i n g i s thus accelerated. An attempt has been made i n the various t r i a l s , to simulate commercial handling c o n d i t i o n s , by b r u i s i n g f r u i t and moving i t back and f o r t h from c o l d storage to room temperatures, and b r u i s i n g at d i f f e r e n t i n t e r v a l s , such as occurs r e g u l a r l y i n handling p r a c t i c e s . Bruised and unbruised f r u i t has also been he l d throughout the experiment i n cold storage and at room temperatures. Supplementary data, such as sugar analyses and pressure t e s t s have also been obtained i n the hope of throwing a d d i t i o n a l l i g h t upon the e f f e c t of b r u i s i n g i n j u r y upon the commercial handling q u a l i t i e s of pears. 2. REVIEW OF LITERATURE In the study of the storage of pears, or any other f r u i t s , i t i s e s s e n t i a l to understand the changes i n carbo-hydrate metabolism associated with r i p e n i n g , and the inf l u e n c e of temperature, enzymes, length of storage and other f a c t o r s upon t h i s process. Sugar Changes i n F r u i t Before Picking? As f r u i t approaches maturity on the t r e e , marked changes i n sugar content occur. Bigelow Gore and Howard ( l ) working w i t h apples, found t h a t i n e a r l y summer the t o t a l sugar content of a l l the wi n t e r v a r i e t i e s was low, running from 3 to 4 percent of the weight of the green t i s s u e . In both summer and winter v a r i e t i e s , the percentage of t o t a l sugar increased s t e a d i l y u n t i l the f r u i t was dropping badly. During the e a r l y season, the sugar was l a r g e l y i n the form of reducing sugars, but as the season advanced there was a marked increase i n the amount of sucrose present, as w e l l as an increase i n reducing sugar. that p r i o r to the formation of starch i n apples, the amounts of f r u c t o s e and glucose and sucrose formed were equal. When the synthesis of s t a r c h began, however, the rate of increase of fructose rose r a p i d l y , while that of glucose remained almost constant. When synthesis of s t a r c h had passed i t s maximum rate and was f a l l i n g , the rate of increase of sucrose and glucose rose, while f r u c t o s e remained constant f o r a Kidd and West, (10), working w i t h apples, found 3« short time at a value about three times that of glucose and then f e l l . Sucrose and glucose, they concluded, seemed to be the a l t e r n a t i v e storage m a t e r i a l to s t a r c h . Magness (13) reported that with pears there i s a marked and quite uniform increase i n t o t a l sugar from e a r l y summer u n t i l a f t e r the time of the close of the commercial packing season. He found the increase during the l a t t e r part of the season was due mainly to an accumulation of sucrose, while the e a r l i e r increase was due mainly to reducing sugar. Bigelow Gore and Howard ( l ) report that i n some v a r i e t i e s of apples, at the end of the growing season, the quantity of reducing sugar and of sucrose was approximately equal, while i n others the reducing sugar was approximately double the sucrose i n q u a n t i t y . Ewert (5) found i n l a t e f a l l v a r i e t i e s of pears a marked increase i n sugar, as both seeded and seedless pears approached maturity, but very l i t t l e s t a r c h i n e i t h e r type of f r u i t . Lewis, Magness and Gate (12) l i k e w i s e found w i t h the B a r t l e t t pear a tendency toward an increase i n sugar as the p i c k i n g season advanced. In 1908 Thompson and W h i t t i e r (19) reported the sucrose, f r u c t o s e and glucose f r a c t i o n s of c e r t a i n f r u i t s . In pears, they found f r u c t o s e to predominate, with small amounts of glucose and sucrose. More r e c e n t l y Gerhardt and E z e l l (7) have reported sugar analyses f o r a number of pear v a r i e t i e s , picked at d i f f e r e n t times during the h a r v e s t i n g season. Glucose, i n a l l v a r i e t i e s , reached a maximum concentration i n the f i r s t p i c k i n g , and then decreased during the remainder of the maturation period. Fructose, however, reached i t s maximum concentration during the second harvest period i n the B a r t l e t t , Flemish and Anjou v a r i e t i e s ? while i n Bosc and Cornice fructose increased throughout the e n t i r e harvest range. Sucrose increased r a p i d l y a f t e r the second harvest period, B a r t l e t t and Bosc v a r i e t i e s being p a r t i c u l a r l y high i n t h i s form of sugar by the close of the growing season. Their work suggests t h a t sucrose and fructose represent the accumulative forms of sugar i n maturing pears,' and could have f o r t h e i r common source the h y d r o l y s i s of s t a r c h . The r a t i o of glucose to fructose increased w i t h m a t u r i t y i n a l l v a r i e t i e s studied. Furthermore, t h i s r a t i o changes for the d i f f e r e n t v a r i e t i e s , being the highest i n the case of Cornice. An explanation f o r the increase i n sugars associated w i t h approaching maturity, l i e s i n the gradual conversion of st a r c h over i n t o sugars. Bigelow Gore and Howard ( l ) found that w i t h apples the starch content of the f r u i t i n terms of percent of the green weight, reached i t s highest point i n the summer v a r i e t i e s i n June, and i n the winter v a r i e t i e s i n J u l y . The a c t u a l t o t a l q u antity of s t a r c h per apple, how-ever, d i d not reach i t s maximum u n t i l much l a t e r , about mid-August i n the winter v a r i e t i e s . From t h i s time forward there was a decrease not only i n percentage composition of st a r c h , but i n a c t u a l s t a r c h per apple, i n d i c a t i n g that there was an ac t u a l s t a r c h h y d r o l y s i s going on a f t e r t h i s date. With starch h y d r o l y s i s there was a sharp increase i n sucrose, i n d i c a t i n g that the sugar storage form which replaces the atarch as the f r u i t matures i s p r i m a r i l y sucrose. In t h i s connection, i t i s i n t e r e s t i n g to consider the s t a r c h and sugar analyses reported by Browne (3) f o r Baldwin apples. The sta r c h analyses were as f o l l o w s : -very green, Aug. 7th - 4.14 percent of the green weight green, Sept. 13th - 3.67 percent " " " " r i p e , Nov. l ^ t h . - .17 percent " " " " overripe, Dec. l ^ t h - none. During the same period, t o t a l sugar increased from 8.03 per-cent, green weight, i n very green apples, to 14.5 percent i n r i p e , and 14 percent i n overripe apples. Sugar Changes A f t e r Ripening:-removal from the t r e e , i t i s important to understand the d i r e c t i o n of i t s metabolic processes, which terminate i n rip e n i n g and f i n a l l y breaking down of the t i s s u e . Magness and D i e h l (16) found w i t h apples, that the chemical changes i n progress when f r u i t i s picked from the tree continue mainly i n the same d i r e c t i o n as before p i c k i n g , though the rate of the various changes may not be the same. From t ime of p i c k i n g forward, they reported that there i s a continuous drop i n a c i d i t y , and the st a r c h present i n the f r u i t changes qu i c k l y to sugar. They also found a marked increase i n sucrose during the time between p i c k i n g and f u l l r i p e n i n g of the same f r u i t . This increase was even more marked i n l a t e than e a r l y picked f r u i t . Following completion of t h i s Since f r u i t continues as a l i v i n g e n t i t y a f t e r i t s change there i s l i t t l e f u r t h e r v a r i a t i o n i n t o t a l sugars, even though there i s undoubtedly a very small l o s s due to r e s -p i r a t i o n . Even t h i s small l o s s , they suggest, may be replaced by a c q u i s i t i o n s from p e c t i n m a t e r i a l s . Kidd and West (9) found i n senescent apples, a decrease i n t o t a l sugars and a h y d r o l y s i s of cane sugar to reducing sugars. Magness and Burroughs (15)» working, w i t h apples, also showed that there i s a sharp increase i n sugars a f t e r p i c k i n g , due to starch being transformed to sugar. Bigelow Gore and Howard ( l ) found that as the f r u i t was h e l d i n storage there was a continuous decrease i n percent of sucrose, and a corresponding increase i n reducing sugar. Ewert (5) found that cane sugar was very seldom present i n r i p e pears, i n the v a r i e t i e s he studied. On the other hand, Magness and B a l l a r d (14) working with B a r t l e t t pears from the Sacramento and Santa C l a r a d i s t r i c t s of C a l i f o r n i a , and the Yakima d i s t r i c t s of Washington, found that f r u i t s picked both green and mature, increased i n sucrose content from p i c k i n g to r i p e n i n g . In f a c t , the increase i n sucrose content was on the average double that at p i c k i n g time. That t h e temper-ature at which f r u i t i s ripened in f l u e n c e s the t o t a l sugar content of pears, was shown by Magness (13). He found that pears ripened at 70° P. contained the highest, and those ripened at 40° P. the lowest, amount of sugar, while f r u i t ripened at temperatures between 40° and 70° P. contained intermediate amounts• . 7 -Role of Enzymes i n Ripening8-I t i s g e n e r a l l y assumed that the h y d r o l y s i s of starch and sucrose i n t o reducing sugars i s e f f e c t e d through the agency of enzymes. Magness (13) considers enzyme a c t i o n to he governed by temperature changes and observes, "That i t i s an i n t e r e s t i n g p o s s i b i l i t y that the temperatures which r e t a r d r i p e n i n g may be s u f f i c i e n t to i n h i b i t enzyme a c t i o n . " Thatcher (18) could not f i n d the enzyme d i a s t a s e i n r i p e n i n g apples, and reported that diastase seemed to disappear w i t h the disappearance of s t a r c h . Neither oould he f i n d invertase In apple t i s s u e , despite the f a c t that numerous workers have shown a decrease i n sucrose, accompanied by an increase i n reducing sugars, as apples and pears r i p e n . The enzyme catalase seems to be associated w i t h r e s p i r a t i o n and general metabolic a c t i v i t y i n p l a n t s . Magness and B a l l a r d (14) studied the amount of catalase present i n pear t i s s u e i n r e l a t i o n to the r e s p i r a t i o n a c t i v i t y of the f r u i t . They found that catalase content increased f o r a time as the f r u i t ripened, but then decreased much sooner than d i d the r e s p i r a t i o n r a t e . They concluded that the marked increase i n r e s p i r a t i o n as pears r i p e n could not be associated w i t h the production of c a t a l a s e , as the causal agency. S i m i l a r work by Magness and Burroughs (15) on apples, revealed that catalase a c t i v i t y of apples i s not associated with the r e s p i r a t o r y a c t i v i t y of the f r u i t at the p a r t i c u l a r time that catalase was determined, but seemed to be associated with the t o t a l r e s p i r a t i o n that had occurred previous to the 8 -making of the oatalase determination. Gatalase was also found to he associated w i t h the a c i d i t y of the f r u i t , the catalase i n c r e a s i n g as the a c i d i t y decreased. From the r e s u l t s secured, no d i r e c t a s s o c i a t i o n between catalase a c t i v i t y and i n t e n s i t y of r e s p i r a t i o n of apples seemed to e x i s t . I t seems hard to understand how these various h y d r o l y t i c sugar changes occur without the apparent agency of d i a s t a s e , invertase or catalase, because such changes are u s u a l l y associated w i t h enzyme a c t i v i t y . I t i s p o s s i b l e that the a c i d present i n the f r u i t might be responsible f o r i n v e r t i n g the cane sugar, but u n t i l more d e f i n i t e information i s a v a i l a b l e , i t i s hard to form any conclusions. F r u i t R e s p i r a t i o n Measured by Carbon Dioxide Production;-Undoubtedly the most r e l i a b l e means of studying f r u i t r e s p i r a t i o n and r i p e n i n g i s by means of the amount of carbon dioxide r e s p i r e d by the f r u i t . Since r e s p i r a t i o n i s dependent upon the breaking down of sugars i n t o carbon dioxide and water, and r i p e n i n g involves a h y d r o l y s i s of s t a r c h , i n v e r t sugar and p e c t i n substances i n t o simpler carbohydrate m a t e r i a l s f o r r e s p i r a t i o n purposes, the carbon dioxide given o f f by f r u i t i n r e s p i r a t i o n should be an accurate index of the r a t e of r i p e n i n g . Magness and B a l l a r d (14) found t h a t the r a t e of r i p e n i n g seemed to p a r a l l e l the carbon di o x i d e output of pears. A number of workers have used t h i s method as an index f o r measuring ra t e of r i p e n i n g of f r u i t . The f r u i t i s enclosed i n containers with an intake and o u t l e t . A continuous stream of carbon d i o x i d e - f r e e a i r i s drawn i n t o the container and passed out through a potassium hydroxide or barium hydroxide s o l u t i o n , to remove the carbon dioxide given o f f by the f r u i t . Another method f o r determining carbon dioxide r e s p i r a t i o n i s to enclose f r u i t i n a container and take analyses of the enclosed a i r w i t h a gas a n a l y s i s apparatus. E f f e c t of Temperature and Length of Storage on R e s p i r a t i o n : -The work of Gore (8) w i t h apples, e s t a b l i s h e d that the rate of e v o l u t i o n of carbon dioxide increased w i t h temperature VaritHoff r u l e , i . e . , the rate increased between two to three times w i t h each r i s e i n temperature of 10° C. Magness and Burroughs (15) at the Marble Laboratory, Pennsylvania, found with Winesap and Baldwin apples, res-p i r a t i o n was 7 to 10 times as great at 65° to 68° F. as at 32° F. Magness and B a l l a r d (14) also studied the rate of carbon dioxide e v o l u t i o n of B a r t l e t t pears at d i f f e r e n t temperatures. In f r u i t h e l d at 59° ^> there was a marked a c c e l e r a t i o n i n the output of carbon dioxide from the time the f r u i t was picked, u n t i l the time i t was s o f t yellow r i p e . This increase i n rate was so great t h a t i n c e r t a i n instances the highest rate of output was seven times the i n i t i a l rate at the same temperature. They found that there was no a c c e l e r a t i o n i n r e s p i r a t i o n of pears h e l d at 30° F. a f t e r more than four months storage. At 37° F. they found a s l i g h t a c c e l e r a t i o n i n the rate of carbon dioxide e v o l u t i o n during the one month that t h e i r f r u i t was h e l d at t h i s temperature * Continuing t h e i r observations, they found that B a r t l e t t s would r i p e n about twice as r a p i d l y at 37° P» as they would at 30° JT. When f r u i t was moved from 3°° to 60° j?., however, the i n i t i a l r ate of CO2 e v o l u t i o n was about equal to what the rate would have been i f the f r u i t had been h e l d at 60° j?. from p i c k i n g time u n t i l a quantity of carbon d i o x i d e equals to the t o t a l amount that had been given o f f at ^0° J7 . had been evolved. This data would seem to suggest t h a t w h i l e the f r u i t was i n a c t i v e at low temperature, the production of enzymes (or whatever substances cause the increased rate'of r e s p i r a -t i o n i n f r u i t ripened at higher temperature) continued normally, and such substances accumulated i n the t i s s u e s , causing immediate and intense a c t i v a t i o n of r e s p i r a t i o n when the f r u i t was removed to room temperature. This may be the explanation why cold storage f r u i t ripens so r a p i d l y a f t e r removal from c o l d storage to room temperature (6). Osborne (17), working w i t h apples, also found a d i r e c t a s s o c i a t i o n between increase i n temperature and increase i n r e s p i r a t i o n . An i n t e r e s t i n g point i n connection w i t h the e f f e e t of temperature on r e s p i r a t i o n , i s the work of Magness (13) and Magness and Burroughs (15) on the composition of the gas i n the i n t e r c e l l u l a r spaces of apples h e l d at d i f f e r e n t temperatures. They found, at low temperatures, that carbon dioxide was low i n proportion to oxygen content i n the i n t e r -c e l l u l a r spaces, whereas at high temperatures the r e l a t i o n was exactly reversed. This c o n d i t i o n , however, was found to be influenced somewhat by v a r i e t y , f o r at 65° 'JT. the i n t e r n a l gas of Winesaps under t e s t , contained f u l l y double the - 11 -carbon d i o x i d e , and not over h a l f the oxygen found i n Baldwins at the same temperature. This r e s u l t was explained on the basis of the tougher and l e s s permeable s k i n of Winesap apples. Maturity at P i c k i n g i n R e l a t i o n to Carbon Dioxide Outputz-I t would seem reasonable i n view of the d i s c u s s i o n on carbohydrate changes i n f r u i t , before and a f t e r p i c k i n g , that the maturity of the f r u i t at harvesting should influence subsequent r e s p i r a t i o n . Burroughs (4) made a number of pi c k i n g s of apples extending over a wide season, and observed that during the p o s s i b l e commercial p i c k i n g season f o r each v a r i e t y , the i n i t i a l r ate of r e s p i r a t i o n of successive samples di d not increase much. However, l a s t picked samples of a l l v a r i e t i e s , except Northern Spy, showed a marked increase. He found that immaturely picked Wageners and Baldwins, stored at 32° F. immediately a f t e r p i c k i n g , r e s p i r e d at an abnormally high rate when t r a n s f e r r e d to 68.5° F. The r a t e , a f t e r removal, was i n some cases a c t u a l l y greater than that of f r u i t picked at the same time and held at 68.5° P. f o r an equal period. Injury to F r u i t i n R e l a t i o n to Carbon Dioxide Output:-Magness and Burroughs (15) made rather an extensive study of the e f f e c t of b r u i s i n g and c u t t i n g f r u i t upon i t s r e s p i r a t i o n r a t e . B r u i s i n g was severe, being accomplished by pressing and r o l l i n g the f r u i t upon a smooth board u n t i l p r a c t i c a l l y the whole surface of the f r u i t was softened to a depth of one eighth to one quarter of an i n c h . Where i n c i s i o n s were made into the f r u i t , only r e l a t i v e l y small - 12 -numbers of i n j u r e d c e l l s were involved. Carbon dioxide r e s p i r a t i o n determinations were made at two temperatures, 32° and 65° P« At low temperature, r e s p i r a t i o n was increased more by b r u i s i n g than by c u t t i n g the f r u i t , whereas at 65° E. the reverse was t r u e . Their f i n d i n g s i n general i n d i c a t e d that any i n j u r y to the f r u i t markedly increases the r a t e of carbon dioxide r e s p i r a t i o n . This increase i s much greater i n p r o p o r t i o n to the amount of t i s s u e i n j u r e d , i f the i n j u r y c o n s i s t s i n a break i n the s k i n , rather than b r u i s i n g only. They showed, however, that the e f f e c t of b r u i s i n g i n i n c r e a s -ing carbon dioxide output i s marked f o r a time, but then diminishes r a p i d l y . On the other hand, there was l i t t l e reduction i n rate of r e s p i r a t i o n of the f r u i t w i t h skins cut during the time under t e s t . This i s probably accounted f o r by the b e t t e r a e r a t i o n of the underlying t i s s u e than i s afforded when the f r u i t i s bruised. Osborne (17)» working wi t h Wagener apples, found a small increase i n r e s p i r a t i o n i n response to s l i g h t b r u i s i n g i n j u r y . MATERIALS AM? METHODS' F r u i t Used; The pears used i n the experiments were grown on the Dominion Experimental S t a t i o n , Summerland, B. C. The v a r i e t i e studied were B a r t l e t t , Bosc, Anjou and Winter N e l l s . The pears were harvested at correct maturity and placed i n storage at 32° P., w i t h i n a day or two of p i c k i n g . The harvesting dates were as f o l l o w s : - B a r t l e t t , Aug. 29th; - 13 -Boso, Sept. 21stj Anjou, Oct. 5th, and YiTinter N e l i s , Oct.26th. As required, the f r u i t was removed from c o l d storage and shipped to the U n i v e r s i t y of B r i t i s h Columbia from Summer-land, a t r i p of one day. As soon as the f r u i t a r r i v e d i t was placed immediately i n storage at 32° F. and h e l d at t h i s temperature u n t i l used f o r experimental purposes. The f r u i t of the Bosc, Anjou and Winter N e l i s v a r i e t i e s a r r i v e d i n p e r f e c t , f i r m green c o n d i t i o n . The B a r t l e t t s , however, which had been h e l d i n storage f o r more than f i v e weeks before shipping, and were shipped during a f a l l "hot s p e l l " , a r r i v e d at the U n i v e r s i t y i n a somewhat ripened c o n d i t i o n , approaching t h e i r c l i m a c t e r i c . Storage F a c i l i t i e s : -The f r u i t used i n t h i s experiment was h e l d at room temperature and at 32° F. The Plant N u t r i t i o n Laboratory at the U n i v e r s i t y , heated by steam, and h e l d at around 22° C. was used f o r h o l d i n g f r u i t at room temperature, while f r u i t held at 32° F. was kept i n the cold storage plant of the Vancouver Ice and Cold Storage Company. The temperature i n o the storage pl a n t d i d not vary from 32 F. more than h a l f of one degree at any time during the storage p e r i o d . Humidity c o n t r o l was not necessary at e i t h e r temperature, since the f r u i t was enclosed i n sealed cans, and created i t s own humidity conditions during r e s p i r a t i o n . Experimental Equipmenti-The f r u i t used i n the r e s p i r a t i o n t e s t s was en-closed i n g a l l o n cans w i t h a i r - t i g h t l i d s . Through a hole - 14 -i n each l i d was f i t t e d a rubber cork, bored to i n s e r t a glass tube. The end of the gla s s tube, extending i n t o the can, was join e d to a piece of rubber tubing reaching to the bottom of the can. The end of the glass tube extending above the l i d was l i k e w i s e f i t t e d w i t h a short piece of rubber tubing, closed w i t h a burette clamp. When a sample of the gas w i t h i n the can was required f o r a n a l y s i s , the clamp was removed, and a p o r t i o n of the gas drawn o f f i n t o an Orsat apparatus. Plan of Experiments:-The f r u i t was given a number of d i f f e r e n t treatments intended to simulate conditions involved i n commercial hand-l i n g . Bruised f r u i t was compared w i t h unbruised f r u i t h e l d at 32° P. and at room temperatures, and c e r t a i n l o t s of pears were removed from 32° P. to room temperature at i n t e r v a l s , and then replaced at low temperatures again. B r u i s i n g was accom-p l i s h e d by dropping the pears onto a hard surface from a uniform height of three f e e t . Approximately one kilogram of f r u i t was placed i n each can, the exact weight being accurately determined. Carbon dioxide r e s p i r e d by the f r u i t , was determined each day i n l o t s h e l d at room temperature, and twice a week i n those l o t s h e l d at 32° P. The treatments given the various l o t s of f r u i t of each v a r i e t y , and t h e i r analogy to commercial handling p r a c t i c e are given below. Treatments 1, 2 and 3 represent pears sent immediately to market,, and allowed to ripen at room temperature i n stores, warehouses, or homes. - 15 -Treatment I t - Bruised and held i n cans at room temperature u n t i l r i p e . Treatment 2t- Not bruised and held i n cans at room temperature u n t i l r i p e . Treatment 3?- Held i n cans at room temperature f o r two weeks, then b r u i s e d and h e l d u n t i l r i p e . Treatments 4, 5 and 6 represent pears placed immediately__in  cold storage a f t e r p i c k i n g , and bruised; b e f o r e _ o r _ a f t e r _  entering the storage. Treatment 4;- Bruised and h e l d i n cans at 32° F. throughout ™ the experiment. Treatment 5s- Not bruised and held i n cans at 32° ^« through-out the experiment. Treatment 6 : - Held three weeks at 32° F. i n cans and then bruised and h e l d throughout the experiment at 32° F. Treatments 7. 8 and 9 represent f r u i t c o l d stored i n the Okanagan, then shipped i n u n r e f r i g e r a t e d cars to market and replaced i n c o l d storage againj_ then removed again from s_torage f o r a few days and r e - s t o r e d o no e more. Such f r u i t receives b r u i s i n g i n different__sta,ges of i t s handling. Treatment 7«- Not br u i s e d and h e l d i n cans at 32° F. through-out the experiment, except when removed f o r short i n t e r v a l s to room temperature. Treatment 8 ; - Held two weeks at 32° F. i n cans and then bruised and removed to room temperature f o r a few days and replaced i n 32° F. storage, and removed and replaced again a second time a f t e r a f u r t h e r i n t e r v a l of two weeks. Treatment 9 Bruised and h e l d i n cans at 32° F. f o r two weeks, then removed to room temperature f o r a few days and replaced at 32° F. and removed and replaced again a second time, a f t e r a f u r -ther i n t e r v a l of two weeks. - 16 -In a d d i t i o n to r e s p i r a t i o n t e s t s , pressure t e s t s and sugar t e s t s were given the f r u i t at various i n t e r v a l s , Loss of weight i n f r u i t during the experiment was determined by weighing the pears at the end of the experimental p e r i o d . The e f f e c t of b r u i s i n g on the dry weight of the t i s s u e was also determined, and m i c r o s c o p i c a l examination of br u i s e d and adjacent normal t i s s u e was made. Experimental Methods  Measurement of Carbon Dioxide t-The carbon dioxide given o f f by the f r u i t was measured i n one of two ways. The f i r s t of these was by Orsat's Gas A n a l y s i s Apparatus, shown i n P l a t e No. 1 and described i n d e t a i l by Winkler and Lunge (20). - 17 -In one absorption tube a 34 percent s o l u t i o n of potassium hydroxide was used f o r measuring the carbon dioxide given o f f by the f r u i t . In a second tube f o r oxygen a n a l y s i s , a combination of a 7 percent s o l u t i o n of p y r o g a l l i c a c i d and a 10 percent s o l u t i o n of potassium hydroxide, was used. The procedure followed i n making a gas a n a l y s i s of a sample of a i r from one of the r e s p i r a t i o n containers was as f o l l o w s . The l e v e l b o t t l e (A) was lowered, f o r c i n g water through the tube (B) into the graduated c y l i n d e r (C), u n t i l a l l the a i r was expelled from the c y l i n d e r . Through the rubber tube (D) connecting the manifold (E) w i t h the r e s -p i r a t i o n container (j?), a 100 cubic centimeter sample of gas was then drawn o f f from the container (F), by removing the burette clamp (G) and lowering the l e v e l b o t t l e (A). By r a i s i n g and lowering the l e v e l b o t t l e (A) approximately 10 times, thereby drawing o f f and f o r c i n g back the sample of a i r from the container (E), the carbon dioxide i n the can was thoroughly mixed with the a i r . Then the 100 cubic centimeter sample of gas to be analysed was drawn o f f from the can, and the manifold (E) was closed by the stopcock at (H). An exact 100 cubic centimeter sample of gas was measured by lowering the l e v e l b o t t l e (A) and by pinching the tube (B) u n t i l the l e v e l of the water stood e x a c t l y at zero. The stopcock (H) was then opened f o r a second to equalize the pressure ins ide and outside the c y l i n d e r , by r e l e a s i n g any excess of gas over 100 cubic centimeters, the l e v e l of the gas s t i l l being maintained i n the c y l i n d e r by - 18 -pinching the rubber, tube. The stopcock (Hj was then closed and the rubber tube (B) released* To obtain the carbon d i o x i d e reading the 100 cubic centimeter sample of a i r i s then forced back and f o r t h through the stopcock ( I ) i n t o the absorption b o t t l e (J) u n t i l a l l the carbon d i o x i d e i s absorbed from the r e s p i r a t i o n sample by the potassium hydroxide. The sample of gas i s then returned to the graduated c y l i n d e r (G) and a reading made of the l e v e l of the gas i n the c y l i n d e r . This i n d i c a t e s i n cubic c e n t i -meters the percent of carbon dioxide removed from the sample. The amount of carbon dioxide r e s p i r e d by the f r u i t i s then c a l c u l a t e d from the volume of the container, l e s s the volume occupied by the f r u i t h e l d i n i t . To obtain an oxygen reading, the balance of the sample of gas i n the c y l i n d e r i s forced through the p y r o g a l l i c a c i d s o l u t i o n i n the second absorption b o t t l e , and a second reading i s made. The d i f f e r e n c e between the f i r s t and second readings represents the oxygen percentage i n the sample. P r a c t i c a l l y a l l the carbon dioxide data were taken by means of Orsat's Apparatus which i s portable, quick and accurate. A f t e r each r e s p i r a -t i o n t e s t the containers were opened and the carbon dioxide flushed out of them, and they were then allowed to stand f o r a few minutes before being closed again. The other method of measuring carbon dioxide was by means of passing a continuous stream of carbon dioxide f r e e a i r over a known weight of pears i n a closed container, and then drawing the a i r through a M i l l i g a n Absorption Tower - 19 -containing a .662 normal s o l u t i o n of potassium hydroxide to remove the carton d i o x i d e . The a i r "before entering the f r u i t container, was freed of carbon dioxide by passing through a soda-lime d e s i c c a t o r , and the suc t i o n force, required to draw the a i r over the f r u i t was supplied by connecting the o u t l e t of the absorption tower by a rubber tube to a f i l t e r pump. An a l i q u o t of the potassium hydroxide s o l u t i o n was t i t r a t e d each day against a .419 normal s o l u t i o n of hydro-c h l o r i c a c i d , w i t h phenolpthalein i n d i c a t o r , to determine the amount of carbon dioxide absorbed by the potassium hydroxide. A d i r e c t t i t r a t i o n w i t h h y d r o c h l o r i c a c i d and phenolpthalein was made po s s i b l e by means of Blasdale's (2) method of p r e c i p i t a t i n g out the potassium carbonate f i r s t w i t h an equivalent amount of barium c h l o r i d e s o l u t i o n . The potass-ium hydroxide s o l u t i o n was renewed d a i l y . Sugar Analyses:-i n t e r v a l s during storage. A j u i c e sample was extracted from equal portions of 5 pears. The j u i c e was expressed i n an ordinary meat chopper, and f i l t e r e d twice through cheesecloth. The sample of j u i c e was then d i l u t e d to one h a l f and tested f o r soluble s o l i d s w i t h a B r i x Spindle. The j u i c e was then d i l u t e d with water to one f o r t i e t h of i t s o r i g i n a l strength f o r chemical sugar determination. From each sample one 100 cubic centimeter sample of j u i c e was inverted w i t h 5 grams c i t r i c a c i d by b o i l i n g ten minutes. A f t e r c o o l i n g , the a c i d i n the j u i c e was n e u t r a l i z e d w i t h a 20 percent. Sugar analyses of pear j u i c e were made at d i f f e r e n t - 20 -s o l u t i o n of sodium hydroxide u n t i l the sample was j u s t n e u t r a l , and d i l u t e d hack to i t s o r i g i n a l volume of 100 cubic centimeters. Invert and reducing sugars were determined by means of Lane and Enyon's copper reduction method, using Fehlings S o l u t i o n s (11). Eehlings A s o l u t i o n was made by d i s s o l v i n g 34.639 grams of copper sulphate i n 5°0 cubic centimeters of water, and Eehlings B s o l u t i o n by d i s s o l v i n g 173 grams Rochelle S a l t and 50 grams sodium hydroxide i n 50 0 cubic centimeters of water. The procedure was as f o l l o w s J - 5 cubic centimeters each of Eehling's A and Eehling's B s o l u t i o n were mixed i n a 250 cubic centimeter Erlenmeyer f l a s k and treated c o l d with 15 to 20 cubic centimeters of the d i l u t e d pear j u i c e . The mixture was then b o i l e d f o r two minutes and three drops of methylene blue were added. S u f f i c i e n t a d d i t i o n a l d i l u t e d j u i c e was then t i t r a t e d i n t o the b o i l i n g mixture u n t i l a l l the copper was reduced, the disappearance of the blue c o l o r from the s o l u t i o n i n d i c a t i n g the complete removal of a l l cupric ions. Erom the f a c t that 50 m i l l i g r a m s of sugar .are required to reduce a l l the copper i n 5 cubic centimeters of Eehling's A s o l u t i o n , the concentration of the sugar i n the j u i c e was c a l c u l a t e d . The f i r s t , or incremental t i t r a t i o n , was followed by a second t i t r a t i o n where the amount of j u i c e required to reduce the copper could be added to w i t h i n one cubic centimeter of the required amount. The end point could then be determined accurately by t i t r a t i n g a few a d d i t i o n a l drops i n t o the b o i l i n g mixture. Where sugar determinations were required i n terms of percentage of f r e s h or dry weight of f r u i t , a l c o h o l - 21 -e x t r a c t i o n s were made,, 30 gram portions of f r e s h pear t i s s u e were b o i l e d i n 250 cubic centimeter Erlenmeyer f l a s k s i n 95 percent e t h y l a l c o h o l , to which was added one cubic centimeter of concentrated ammonium hydroxide, 'i'he f i r s t b o i l i n g was i n 100 cubic centimeters of a l c o h o l f o r 15 minutes, a f t e r which the a l c o h o l e x t r a c t was f i l t e r e d , and the t i s s u e then b o i l e d again twice, f o r 10 minutes each time, i n 75 cubic centimeters a l c o h o l , decanting and f i l t e r i n g the extract each time. The three portions of the a l c o h o l extract were then combined and b o i l e d long enough to evaporate o f f a l l the a l c o h o l . The a l c o h o l f r e e s o l u t i o n was then d i l u t e d to the necessary degree, and treated w i t h Fehling's s o l u t i o n . Pressure Tests The pressure t e s t s were made with the standard B a l l a u f pressure t e s t e r , on the pared f l e s h of the f r u i t , three punches being taken on each f r u i t , and f i v e pears being used f o r a sample. - 22 -RESULTS E f f e c t of B r u i s i n g on Carbon Dioxide R e s p i r a t i o n at Room Temperature. The pears used i n the experiments at room temper-ature were d i v i d e d into three l o t s , Treatments 1, 2 and 3* Treatment 1 f r u i t was b r u i s e d at the s t a r t ; Treatment 2 f r u i t was unbruised and Treatment 3 f r u i t was b r u i s e d a f t e r being h e l d two to three weeks i n the r e s p i r a t i o n containers. The r e s p i r a t i o n data secured are presented i n Tables I and II, and a g r a p h i c a l representation of the r e s p i r a t i o n trend of Winter U e l i s i s shown i n Chart I. Table I shows that w i t h the Bosc v a r i e t y there i s no s i g n i f i c a n t i n f l u e n c e of b r u i s i n g upon r e s p i r a t i o n i n t e n s i t y . Due to the l e n g t h of the runs, i n most cases, being too long, the data f o r t h i s v a r i e t y shows more than anything else the depressing e f f e c t of carbon dioxide accumulation i n the con-t a i n e r s upon r e s p i r a t i o n . Treatment 3> i n v o l v i n g delayed b r u i s i n g was not given to t h i s v a r i e t y . The r e s p i r a t i o n data f o r Winter Efelis l i k e w i s e shows no s i g n i f i c a n t e f f e c t from b r u i s i n g . Treatment 3 f r u i t r e s p i r e d f a s t e r than the f r u i t of e i t h e r Treatment 1 or 2, u n t i l almost the end of the experiment, and then dropped o f f suddenly f o r no accountable reason. The b r u i s i n g given Treatment 3 f r u i t toward the end of the t e s t c e r t a i n l y does not seem to have induced t h i s e f f e c t . There does not appear to be much c o r r e l a t i o n between f l u c t u a t i o n s i n temperature and r e s p i r a t i o n i n t e n s i t y of the f r u i t , perhaps due to carbon - 23 -TABLE NO. I Rate of Carbon Dioxide R e s p i r a t i o n of Bosc and Winter N e l i s at _____ Room Temperature  Temper- Length % C 0 2 Run ature of Run i n Con-No. (deg.C) (hrs.) tainer# c.c. C O 2 per Kilogram Hr. Treat . 1 Treat.2 Treat . 3 Remarks Bosc 20 25 7.7 10.0 2" 23 50 13.4 8.7 3 18 47 9.2 6.4 4 19 48 14.8 10.0 5 27 51 10.0 6.4 6 23 52 11.0 7 17 48 12.6 8 20 23 8.2 9 20 25 8.4 Winter N e l i s 1 20 20 5.0 2 20 47 9.0 3 22 23 6.0 4 25 24 6.0 5 22 24 8.4 6 22 22 7*0 7 22 24 8.8 8 20 70 14.0 9 22 26 10.6 10 22 24 10.4 11 20 22 •8.8 12 22 26 15.8 13 26 49 13.7 14 23 23 13.4 16.3 8.5 11.6 10.9 8.4 6.5 8.8 8.4 11.8 10.7 12.4 6.8 13.7 14.6 13-5 20.5 9.4 8.8 9.2 6.5 9.6 9.7 19.0 8.6 10.1 10.2 8.0 6.0 8.8 9.1 12.7 14.1 13.0 7.2 14.5 15.4 XX • 2 19.8 10.6 7. 9-XX e 11. 12. 16. 16. 9 . 4 0 1 4 4 1 I 16. 21. 17. 23. 13. x . Ripe Resp. depressed by COp accum-u l a t i o n . Resp. depressed by COp accum-u l a t i o n . I9 .6 I8.9 15.8 Resp. depressed by CO2 accum-u l a t i o n . Bruised, Treat.3; Pears r i p e . x Resp. depressed by CO2 accum-u l a t i o n . # % CO2 f o r Treatments 2 and 3 corresponds to Treatment 1. x Some unknown f a c t o r depressed r e s p i r a t i o n on t h i s run. Interpolated f i g u r e used on graph. Treatment 1 - Bruised at s t a r t . Treatment 2 - Uhbruised. Treatment 3 - Bruised 2 to 3 weeks a f t e r s t a r t of t e s t . 24 ~ T A B L E D . I I Hate of Carbon Dioxide R e s p i r a t i o n of Anjou at Room Temperature. Temper- Length % C O 2 c o . CO^ , per Kilogram Hr. Run ature of Run i n Con- ~ No. (deg.C) (hours) tainer# Treat . 1 Treat.2 Treat.3 Remarks An.jou , 1-- 20 70 6.6 3.1 3.9 5.0 2 23 74 7.2 3.2 5.1 5.6 3 18 47 4.2 3.0 6.0 6.5 4 22 49 5.1 3.4 6.0 6.3 5 27 50 4.2 2.8 5.8 5.3 6 23 22 2.2 3.3 6.1 6.2 7 17 48 3.6 2.5 5.5 4.8 8 20 24 2.0 2.8 .3.3 4 . 4 9 19 24 3-o 4 . 1 4.3 3-9 10 21 2-5 2.2 2.9 6.4 5.8 11 23 27 4.8 5.9 4.9 4.9 12 23 47 6.0 4.2 5.1 5.3 13 22 26 4.0 5.1 6.4 7.1 14 25 22 3.8 5.8 7.2 15 22 24 5.2 7.2 7.3 7.5 16 22 22 5.O 7.5 8.2 8.1 17 23 24 4.6 6.3 7.0 9.1 18 20 70 10.1 4.8 5.3 £.2 19 22 25 8.3 11.0 9.6 11.0 20 ... 22 24 , 7.6 10.5 9.7 9.3 21 20 24 7.2 9.9 8.0 8.3 22 22 26 7.2 9.2 10.6 8.9 23 26 49 11.0 7.4 5.9 7.1 24 23 23 7.2 10.4 10.4 10.9 25 25 25 8.6 11.4 9.4 9.0 Treat . 3 Bruised. Resp. depressed by CO2 accumulation Ripe. Resp. depressed by CO2 accumulation # % CO2 f o r Treatments 2 and 3 corresponds to Treatment 1. Treatment 1 - Bruised at s t a r t . Treatment 2 - Unbruised. Treatment 3 - Bruised two weeks a f t e r s t a r t of t e s t . - 25 -dioxide accumulation overshadowing t h i s e f f e c t . I t i s i n t e r -e s t i n g to note the i r r e g u l a r rate of r e s p i r a t i o n of the f r u i t of t h i s v a r i e t y , f o r a l l the treatments, i n d i c a t i n g that the f r u i t r e s p i r e s i n "spurts". This i s quite i n keeping w i t h the p e c u l i a r i t y of uneven r i p e n i n g e x h i b i t e d to a greater or l e s s degree by a l l v a r i e t i e s of pears. The data i n Table I I i n d i c a t i n g the r e s p i r a t i o n trends of Anjou pears under d i f f e r e n t treatments, show again no c o r r e l a t i o n between e i t h e r i n i t i a l or delayed b r u i s i n g and rate of r e s p i r a t i o n . In f a c t , the bruised f r u i t of Treatment 1, showed a c o n s i s t e n t l y lower r e s p i r a t i o n rate than e i t h e r Treatment 2 or 3 f o r the f i r s t h a l f of the .experiment, but during the l a t t e r h a l f rose to approximately the same l e v e l of the other f r u i t . These data suggest st r o n g l y that f a c t o r s other than b r u i s i n g treatment are f a r more important i n t h e i r e f f e c t on r e s p i r a t i o n , than b r u i s i n g treatment i t s e l f . I t i s a w e l l known f a c t that i n d i v i d u a l apples, e x t e r n a l l y s i m i l a r , show great d i s s i m i l a r i t y i n t h e i r r e s p i r a t i o n rates under given c o n d i t i o n s . I t i s more than l i k e l y that t h i s same i n d i v i d u a l -i t y e x i s t s i n pears, and that the pears used i n Treatment 1 happened to be mostly, or a l l , low r e s p i r a t i o n i n d i v i d u a l s . This i s a probable explanation f o r the behavior of the Anjous i n Treatment 1. x Kidd, F. and C. West. Report of the Pood I n v e s t i g a t i o n Board, pp. 40 - 41, H i s Majesty's St a t i o n e r y O f f i c e , London, 1925, 1926. - 26 -R e s p i r a t i o n at Room Temperature Under Gonditions of Good Aerat i o n . . In order to confirm the r e s p i r a t i o n r e s u l t s secured by Orsat's Apparatus w i t h f r u i t enclosed i n a i r t i g h t containers (Tables I and I I ) , a second set of experiments were c a r r i e d out w i t h the Winter N e l i s v a r i e t y . The f r u i t was enclosed i n a i r t i g h t cans w i t h an i n l e t and o u t l e t through which a continuous stream of carbon d i o x i d e - f r e e a i r was passed over the pears. The carbon dioxide given o f f by the f r u i t was absorbed from the out-passing a i r i n a M i l l i g a n Absorption Tower containing a potassium hydroxide s o l u t i o n . A stream of a i r was passed through the container at a ra t e s u f f i c i e n t to change the a i r completely every t h i r t y - f i v e minutes. Under such conditions p o s s i b i l i t i e s of carbon dioxide accumulation i n the containers. depressing r e s p i r a t i o n , were eliminated. Bruised and unbruised pears were used I n the experiment, and, i n a d d i t i o n , pears which received a shallow cut h a l f an inch wide on both sides were compared. The f r u i t used had been h e l d i n c o l d storage at 0°G. f o r f i v e weeks p r i o r to the s t a r t of the experiment. The r e s u l t s secured are presented i n Table I I I . - 27 -TABLE m. I l l tInfluence of B r u i s i n g and Cutting Winter M e l i s Pears Upon Their Rate of Carbon Dioxide R e s p i r a t i o n and Loss of Weight at Room Temperature. Length of Run (Hours) 23.5 23.O 20.5 27.0 23.5 T o t a l Ave. c.c. C O Q per Kilogram Hour Bruised Gut Check 41.8 34.7 32.9 34.0 43.3 41.3 37.7 35.2 46.1 35.6 38.6 35.4 48.4 44.4 33.7 186.7 37.34 i 1.45 195.9 200.5 39.18 t I .38 40.1 * 1.87 Loss of Weight During Test (Grams) Before t e s t 981,5 A f t e r t e s t 970.5 Loss % 1.12 968 960 .62 956 943 1.36 This data shows c l e a r l y the wide v a r i a b i l i t y i n r e s p i r a t i o n i n t e n s i t y that occurs d a i l y i n d i f f e r e n t l o t s of f r u i t . - 28 -On the f i r s t "run" the bruised f r u i t r e s p i r e d the most r a p i d l y ; on the second run, the cut f r u i t , a n d on the t h i r d run, the check f r u i t was the highest. Of the other two runs the cut f r u i t was highest f o r one and the bruised f r u i t f o r the other. I t would appear, therefore, t h a t the d i r e c t i o n of the r e s p i r a t i o n trend of pears, bears no r e l a t i o n to b r u i s i n g or c u t t i n g i n j u r y , but rather i s influenced (or overshadowed) by v a r i a b i l i t y i n the r e s p i r a t i o n mechanism of the i n d i v i d u a l pears themselves. In f a c t the cheek f r u i t r e s p i r e d f a s t e r on the average during the f i v e days of the experiment than e i t h e r the cut or bruised f r u i t . On s t a t i s t i c -a l a n a l y s i s , however, t h i s d i f f e r e n c e i n r e s p i r a t i o n i n t e n s i t y i s not s i g n i f i c a n t , nor i s there any s i g n i f i c a n t d i f f e r e n c e i n the degree of v a r i a b i l i t y of the three samples of f r u i t . On the basis of the percentage l o s s of weight of the f r u i t during the experiment, no c o r r e l a t i o n seems to e x i s t between t h i s f a c t o r and r e s p i r a t i o n r a t e . I t i s true that the check f r u i t which r e s p i r e d the f a s t e s t also l o s t the greatest amount of weight (1.36^), but on the other hand the cut f r u i t which r e s p i r e d at almost an i d e n t i c a l rate with the check f r u i t l o s t l e s s than h a l f as much weight during the t e s t (,62/&). This r e s u l t seems hard to e x p l a i n , but may be a t t r i b u t e d to the f a c t that the humidity i n the container was maintained by the water given o f f by the f r u i t at a point high enough to i n h i b i t to a large degree water l o s s . Examination of the f r u i t at the end of the treatment showed that the cut portions of the f l e s h showed no moistness and - 29 -were completely dry and c a l l o u s e d over. These data go to show, even more c o n c l u s i v e l y , that pears e x h i b i t marked i n d i v i d u a l i t y i n t h e i r metabolic a c t i v i t y and r e s p i r a t i o n responses. Comparative Rate of R e s p i r a t i o n at Room Temperature f o r D i f f e r e n t V a r i e t i e s . The rate of r e s p i r a t i o n of pear v a r i e t i e s d i f f e r s markedly as shown i n Chart I I . The points on t h i s chart were p l o t t e d from the r e s p i r a t i o n rates of the unbruised f r u i t i n Tables I and I I . The Bosc v a r i e t y r e s p i r e d slowly f o r a time, then increased very r a p i d l y to the point where the pears were r i p e , and then dropped o f f i n rate of r e s p i r a t i o n to the l e v e l i t had h e l d p r i o r to the increase preceding r i p e n i n g . Winter N e l i s seemed to r e s p i r e i n "waves" in c r e a s i n g i n i n t e n s i t y u n t i l w e l l beyond the r i p e n i n g point, before beginning to d e c l i n e . The Anjou v a r i e t y , on the other hand, increased i n r e s p i r a t i o n g r a d u a l l y f o r the f i r s t few runs, then f e l l o f f s l i g h t l y and increased again i n waves of i n t e n s i t y u n t i l a maximum rate was reached i n three days a f t e r the f r u i t had become r i p e . A f t e r t h i s point of maximum r e s p i r a t i o n , the curve f e l l o f f again s l i g h t l y , I t i s i n t e r e s t i n g to note the c o r r e l a t i o n between the r e s p i r a t i o n rates of these three v a r i e t i e s , and t h e i r commercial handling q u a l i t i e s . Bosc i s a v a r i e t y which ripens very f a s t once i t s t a r t s , but then remains i n good eating condition f o r a week or more a f t e r r i p e n i n g . The f a c t t h a t i t drops o f f r a p i d l y i n r e s p i r a t i o n a f t e r the r i p e n i n g point i s the probable explanation why i t keeps i n good condition f o r - 30 -some time a f t e r the r i p e n i n g point has been reached. Winter ITelis i s an i n t e r e s t i n g v a r i e t y , f o r while , i t i s one of the longest keeping pears, often keeping i n 0°C. storage i n good co n d i t i o n f o r s i x or seven months, yet when removed to room temperature i t ripens very r a p i d l y , and does not remain i n good eating c o n d i t i o n f o r more than a week a f t e r becoming r i p e . This very r a p i d rate of r i p e n i n g c o r r e l a t e s p e r f e c t l y with the h i g h r e s p i r a t i o n i n t e n s i t y of t h i s v a r i e t y continuing w e l l beyond the r i p e n i n g point, as shown i n Chart I I . The f a c t t h a t Winter ITelis pears continue to r e s p i r e r a p i d l y a f t e r r i p e n i n g has taken place i s a probable explan-a t i o n of why they do not hold i n eating c o n d i t i o n long a f t e r r i p e n i n g . The g r a d u a l l y i n c r e a s i n g , but low r e s p i r a t i o n i n t e n s i t y of the Anjou v a r i e t y explains admirably the long keeping q u a l i t i e s of t h i s pear. The f a c t that i t ripens slowly, and keeps i n good con d i t i o n three weeks or more a f t e r r i p e n i n g , accounts f o r i t s p o p u l a r i t y among f r u i t dealers. The data i n Chart II i n d i c a t e that t h i s v a r i e t y takes twice as long to ripen and r e s p i r e s about h a l f as f a s t as e i t h e r Bosc or Winter N e l i s . - 31 -E f f e c t of Carbon Dioxide Accumulation Upon Depression of R e s p i r a t i o n .  Where r e s p i r a t i o n readings w i t h the d i f f e r e n t l o t s of f r u i t were not taken d a i l y and the carbon dioxide accumu-l a t e d i n the cans f o r two or three days (such as occurred over a weekend), a marked depression i n r e s p i r a t i o n i n t e n s i t y of the f r u i t r e s u l t e d . This data i s presented i n Table IV, which shows normal r e s p i r a t i o n before and a f t e r the carbon dioxide accumulation, and the concentration of carbon dioxide which caused the depression. TABLE IV. Depression of R e s p i r a t i o n at Room Temperature by Carbon Dioxide Accumulation. V a r i e t y Length of Run (hours) .• GO2 cone, i n Resp. Container C • C • GO r\ per Kg.Mr. Bosc Before 22 48 11.0 12.6 I6.3 8.5 A f t e r 23 8.2 11.6 An.jou Before 26 49 6.4 7.2 10.6 5.9 A f t e r 23 6.0 10.4 An.iou Before 24 70 5.1 8.6 7 . 0 5.3 A f t e r 25 6.4 9.6 Winter N e l i a Before 24 70 8.6 14.0 13.0 7.2 A f t e r . 26 10.4 14.5 Winter N e l i s Before 26 49 14- © 2 14.4 19.8 10.6 A f t e r 23 12.0 18.9 With, the Bosc v a r i e t y where the concentration of carbon dioxide i n the container reached 11 percent, increas-i n g the length of the run from 22 to 48 hours r e s u l t e d i n an increase i n the concentration i n the container to only 12 .6%. In other words, when the concentration of the carbon di o x i d e i n the container reached 11 percent the f r u i t ceased to r e s p i r e almost completely. With the Anjou v a r i e t y , depression of r e s p i r a t i o n seemed to occur when the concentration of carbon d i o x i d e exceeded approximately 6 percent where both 49 and 7° hour runs were compared, wi t h 24 hour runs. In the case of Winter N e l l s depression of r e s p i r -a t i o n seemed to occur where the carbon dioxide concentration i n the container exceeded 14 percent. Thus a 26 hour run gave a carbon dioxide concentration of 14.2 percent, while i n c r e a s i n g the length of the run to 49 hours brought the concentration up to only 14.4 percent, i n d i c a t i n g that beyond a concentration of 14 percent Winter N e l i s pears are unable to absorb f u r t h e r oxygen from the atmosphere. I f these data were considered i n terms of carbon dioxide storage of pears, i t i s l i k e l y that a concentration of 7 percent f o r Anjou, 12 percent f o r Bosc, and 14 percent f o r Winter N e l i s would be near the c o r r e c t amount f o r s t o r i n g these v a r i e t i e s . Rate of R e s p i r a t i o n at 0°C. f o r D i f f e r e n t V a r i e t i e s Certain l o t s of f r u i t were h e l d at 0°C. throughout the e n t i r e experiment. Treatment 4 f r u i t was bruised at the - 33 -T A I L S N O . V . gate of Carbon Dioxide R e s p i r a t i o n of B a r t l e t t and Bosc at 0°C. % C0 2 i n Length Containers c.c. C0 o_per Kilogram Hour Run of Run f o r „ ~ — 2 - = ^ - — E a — 1 — IP.. lM§_rJ Treat. 4 ^ Treat. 4 Treat. 5 Treat. 6 Remarks B a r t l e t t 1 2 3 4 7 8 9 Bosc 1 2 3 4 7 8 9 10 i i 12 13 48 71 72 96 97 70 74 96 94 71 96 97 72 72 97 95 94 74 72 96 72 95 4.2 3.6 3.2 4 . 8 4 . 3 4 . 2 4 . 3 4 . 2 7*2 2.0 2.0 2.4 2.5 2.4 2.1 2.2 2.2 2.3 2.4 2.0 2.4 1.8 3.2 1.8 1.6 1.8 1.6 2.1 2.1 1.6 2.8 1.0 . 8 • 9 1.3 1.2 .8 .8 .8 1.2 1.2 .8 1.2 .7 3.6 1.7 1.2 1.6 1.3 1.8 1.6 •3.2 5.6 1.1 1.4 1.0 1.4 1.0 .8 • 9 .9 1.2 1.1 1.3 1.0 4.2 1.7 1.3 2.0 1.2 1.4 3.6 3.1 3*6 1. 1. 1. 1. 1. 1. 1. 1. 1. 1. 9 7 8 l 3 2 1 0 1 1 2 4 0 Treat . 6 Bruised. A l l three yellow. E a t i n g r i p e . Treat.6 Bruised, # % G0 2 f o r Treatments 5 and 6 corresponds to Treatment 4. Treatment 4 - Bruised at s t a r t . Treatment 5 - Unbruised. Treatment 6 - Bruised 2 to 3 a f t e r s t a r t of t e s t . - 3 4 -TABLE NO. VI Rate of Carbon Dioxide R e s p i r a t i o n of Anjou and Winter N e l i s at 0°C. Run Ho. An.jou 1 2 3 4 I 7 8 9 10 n ' 12 13 14 Length of Run (hrs.) % C 0 2 i n Container^ 47 73 71 96 97 72 72 97 96 95 71 95 96 1.8 5.6 3.4 3.7 1.4 1.2 2.6 3.8 2.4 1*8 2.2 3.6 1.6 2.3 c.c. COp per Kilogram Hour Treat . 4 Treat.5 Treat.6 Remarks 1.3 2.5 1.6 1.3 .5 .5 1.2 1.3 .8 .6 1.0 1.2 .7 .8 1.1 2 . 4 1.5 1.5 -.7 .5 . 6 .4 •3 :? .7 . 4 1.3 1.3 1.7 1.5 1.0 .8 ...7 1.0 Treat . 6 Bruised .7 1*3 .7 1.0 .8 .5 Winter N e l i s 1 2 3 4 7 95 94 73 73 95 73 95 2.2 .9 .9 «7 2.4 .9 .9 1.0 2.0 1.0 1.3 .9 2.1 1.2 1.2 •9 2.8 1.1 1.0 1.1 2.2 1.1 1.2 1.8 2 .6 1.0 1.0 1.8 Treat.6 Bruised # $ CO2 f o r Treatments 5 and 6 corresponds to Treatment 4, Treatment 4 - Bruised at s t a r t . Treatment 5 - Unbruised. Treatment 6 - Bruised 2 to 3 weeks a f t e r s t a r t of t e s t . - 35 -b e g i n n i n g o f the exper iment , Treatment 5 f r u i t was unbru i sed and Treatment 6 f r u i t was b r u i s e d 2 to 3 weeks a f t e r p l a c i n g I n s t o r a g e . The r e s p i r a t i o n da ta o f t h i s f r \ i i t i s found i n Tab le s V and V I and i s graphed i n Chart I I I . I t i s i n t e r e s t i n g to note that t h e r e i s ve ry l i t t l e d i f f e r e n c e i n the r e s p i r a t i o n r a t e s o f the d i f f e r e n t l o t s of f r u i t , t a k i n g the data o f the four v a r i e t i e s as a whole . The B a r t l e t t s at the s t a r t of the experiment appeared to be ju s t e n t e r i n g upon t h e i r c l i m a c t e r i c , which probab ly exp l a in s t h e i r h i g h e r i n i t i a l r a t e o f r e s p i r a t i o n . A f t e r f a l l i n g o f f i n r e s p i r a t o r y a c t i v i t y f o r two weeks the f r u i t o f a l l three t reatments rose r a t h e r r a p i d l y i n r e s p i r a t o r y a c t i v i t y , and cont inued on the upward t r e n d u n t i l removed from storage (when r o t s had begun to appear on the p e a r s ) . T h i s l a s t upward t r e n d was a s s o c i a t e d w i t h comple t ion o f r i p e n i n g , the f r u i t when removed be ing i n e a t i n g r i p e c o n d i t i o n . Treatment 6 f r u i t , which was b r u i s e d 22 days a f t e r be ing p l a c e d i n s to rage , showed no apparent response to the t reatment , even though i t was n e a r l y r i p e . The unbru i sed f r u i t , toward the end o f the experiment , showed the h i g h e s t r e s p i r a t i o n ra te o f any o f the t r ea tment s . In the case of the Bosc , Anjou and W i n t e r H e l l s v a r i e t i e s , l i t t l e v a r i a t i o n seemed to occur throughout the e n t i r e experiment i n ra te o f carbon d i o x i d e e v o l u t i o n . The pears even at low temperature appeared to r e s p i r e i n "waves" the same as at room temperature , o n l y the l e n g t h o f a " r e s p i r a t i o n wave" at 0 ° G . was much g r e a t e r , bu t very much l e s s in tense than one at 2 0 ° C. M 3 N oD HISS? "J 13iJ(13>l a3i3wmiw NOU03S ssoyo ayvawvis Y S i l Nl 3QVW Length of consecutive runs — / c m = <4-<3 hours - 36 - • •; With the Anjou v a r i e t y there i s a s l i g h t suggestion that r e s p i r a t i o n i n t e n s i t y was increased f o r a time by delayed . b r u i s i n g (Treatment 6), but i t i s probable that at the time the pears were bruised they were entering upon an upward trend i n t h e i r r e s p i r a t i o n i n any case. In the case of delayed b r u i s i n g of the Winter E e l i s v a r i e t y , there appeared to be quite an upward swing i n r e s p i r a t o r y a c t i v i t y , but whether or not t h i s would have been maintained i s d i f f i c u l t to say. The f a c t t h a t so l i t t l e response was shown through-out the experiment to b r u i s i n g treatment at 0°C. i s hardly s u r p r i s i n g , since i t would be expected that f r u i t at t h i s temperature would show a minimum of response to any k i n d of treatment. E f f e c t of Change of Temperature Upon Respiratory A c t i v i t y C e r t a i n l o t s of f r u i t were held at 0°G. and then removed to room temperature at two to three week i n t e r v a l s f o r a few days. They were then again placed i n cold storage. Three l o t s of f r u i t were compared; Treatment 9 f r u i t being bruised at the s t a r t , Treatment 7 f r u i t being l e f t unbruised and Treatment 8 f r u i t being bruised at the same time as the f i r s t removal to room temperature. When f r u i t was removed from cold storage to room temperature i t was opened up and allowed to stand over night at 2 0 ° C. to warm up before being enclosed f o r carbon dioxide r e s p i r a t i o n measurements. The data secured are presented i n Tables VII and V I I I and represented g r a p h i c a l l y i n Chart IV. The most s t r i k i n g feature of Chart IV i s the - 37 -immediate and intense a c t i v a t i o n of r e s p i r a t i o n i n a l l v a r i e t i e s upon removal from cold storage to room temperatures. This increase i n r e s p i r a t i o n i n t e n s i t y i s even more s t r i k i n g a f t e r the second removal than i t i s a f t e r the f i r s t . Throughout these data there appears to he no p o s i t i v e c o r r e l a t i o n between d i f f e r e n t b r u i s i n g treatments and r e s p i r a -t i o n response w h i l e the f r u i t was held at 0°C.?either before or a f t e r removal to room temperature. Upon removal to room temperature, however, there i s some d i f f e r e n c e i n response from the d i f f e r e n t treatments given the pears. In the f i r s t removal of B a r t l e t t s from 0° C. to room temperature, the f r u i t given the i n i t i a l b r u i s i n g r e s p i r e d at the highest rate while f r u i t b r uised the day a f t e r i t was removed r e s p i r e d at the lowest r a t e , unbruised f r u i t being intermediate between the two. On the second removal, however, unbruised f r u i t r e s p i r e d f a s t e r than the f r u i t bruised at the s t a r t , while f r u i t of Treatment 8, r e c e i v i n g delayed b r u i s i n g , was the slowest of the three. These data suggest again that v a r i a b i l i t y i n the samples of f r u i t themselves influenced r e s p i r a t i o n i n t e n s i t y more than the b r u i s i n g treatment i t s e l f . With the Bosc v a r i e t y r e s p i r a t i o n i n t e n s i t y a f t e r removal to room temperature, showed very l i t t l e d i f f e r e n c e w ith the various treatments. F r u i t r e c e i v i n g b r u i s i n g at the time of the f i r s t removal showed a s l i g h t l y higher r e s p i r a t i o n r a t e , while on the second removal the unbruised f r u i t r e s p i r e d the f a s t e s t . With the Anjou v a r i e t y , f r u i t bruised at the - 38 -TABLE NO. V I I E f f e c t of Change of Temperature from 0° C. to Room Temperature Upon R e s p i r a t i o n I n t e n s i t y of B a r t l e t t and Bosc. Length % C0 2 Run of Run i n Gon-l o . (hrs«) tainer# c.c. COg per Kilogram Hr. Treat,7 Treat , 8 Treat.9 Remarks B a r t l e t t 2 3 4 I 7 8 9 10 i i 48 72 70 97 97 47 96 94 19 25 4.1 3.6 2 . 8 3.5 3.2 8.0 3.6 4 . 8 4.2 1 2 . 0 1 2 . 1 3.5 2.1 1.7 1.5 1.4 16.6% 2.0 2.0 1.9 26.2 20.1 3.6 1.9 3-3 2.3 1.3 11.0 1.7 1.2 2.5 19.7 15.4 3.2 2.3 2 . 3 2.6 2.3 15.2 1.8 2.4 1.6 24.6 17.3 Bosc 1 71 2.0 1.0 .8 , 1.3 2 96 3*8 1.4 l . l 3 97 2.4 .9 1.2 •9 4 72 2.4 1.2 1.2 X & X 5 19 4.9 9.0 l l . O 9*9 6 25 8.4 11.7 12.9 11.4 7 97 3.2 1.2 1.1 1.0 8 95 3*2 1.2 l . l .8 9 93 2.6 1.0 1.2 1.0 10 73 2.2 X © X X B X .9 11 72 2.6 1.3 1.0 1.0 12 24 9.3 13*5 8.6 13.1 13 22 11.2 17.8 15.6 15.8 14 18 7.9 15.3 13.9 14.6 15 72 2.6 1.3 ® 0 1.2 16 95 2.8 1.0 « 5" •9 E r u i t warm when placed i n storage, Treat.8 "bruised. Held at 20° C. Held at 22 C. " " 20° C. E r u i t a l l eating r i p e . Treat . 8 bruised. Held at I 9 0 C. 21° C. Held at 26° C. * • 26° G. «' » 22° C. F r u i t showing yellow. # % C0 2 f o r Treatments 8 and 9 corresponds to Treatment 7< x Only 20 hour run. Interpolated f i g u r e used i n graph. Treatment 7 - Unbruised. Treatment 8 - Bruised 2 to 3 weeks a f t e r s t a r t of t e s t . .Treatment 9 "* Bruised at s t a r t . TABLE HO. V I I I . E f f e c t of Change of Temperature from 0 C. to Room Temperature Upon R e s p i r a t i o n I n t e n s i t y of Anjou and Winter H e l l s . i n c.c. COp per Kilogram Hourr Run of Run Container^ Ho. (hrs.) Treat.7 Treat.8 Treat.9 Anjou 1 48 6'. 7 5.4 4.8 5.2 2 73 2.8. 1.4 1.9 2.0 3. 71 2.8 1.5 1.1 2.0 4 96 4 . 2 1.7 . 8 1.5 5 97 3.7 1.4 . 8 1.0 6 72 1.0 •? l . l 1.5 7 72 X © 2 .6 1.0 X • X 8 20 3,6 6.8 6.5 8.8 9 48 4.4 3.5 4 . 2 6.8 10 97 5.0 2.0 1.4 2.4 i i 95 7.4 2.1 1.5 2 4 X 12 73 1.9 1.0 2 • X 2.1 13 24 4 . 6 7.2 9.0 9.4 14 24 4 . 0 6.3 9.0 12.2 15 16 4 . 0 9.5 10.2 10.6 16 73 7.9 4 . 1 2.2 1.4 17 96 1.0 .4 • 6 1.0 Winter H e l l s 1 2 3 4 I 7 95 94 73 73 9 I 46 97 2.5 1.0 •9 1.0 2.4 1.0 1.0 1.1 2.2 1.1 X • X X • X 2.6 . 1.3 •1.0 1.3 1.0 .4 .9 1.0 9.5 7.8 10.9 9.0 2.8 1.1 «• 0 .8 Remarks F r u i t •warm when placed i n storage. Held at 23° C. Held at 20° C. Held at 26 C. Held at 23° C. Held at 22° C. Showing yellow. Almost eating ripe , Held at 22 u C. # % COp f o r Treatments 8 and 9 corresponds to Treatment 7< Treatment 7 - Unbruised. Treatment 8 - Bruised 2 to 3 weeks a f t e r s t a r t of t e s t . Treatment 9 - Bruised at s t a r t . - 40 -beginning of the experiment r e s p i r e d f a s t e s t upon removal to room temperature both times i t was taken from cold storage. However, a f t e r the f i r s t removal Pthe unbruised f r u i t ? a n d f r u i t r e c e i v i n g delayed b r u i s i n g r e s p i r e d at almost i d e n t i c a l r a t e s , while on the second removal the r e s p i r a t i o n rate of the check f r u i t was decidedly the lower. Due to the l a t e p i c k i n g season of Winter N e l l s , the length of time t h i s v a r i e t y could be studied i n storage was l i m i t e d . Only one removal of f r u i t from cold storage was made and delayed b r u i s i n g i n Treatment 8 was omitted. In other words Treatments 7 and 8 were i d e n t i c a l f o r t h i s v a r i e t y . The f r u i t of Treatment 9 r e c e i v i n g i n i t i a l b r u i s i n g , showed a s l i g h t l y higher r e s p i r a t i o n r a t e , a f t e r removal to room temperature, than that of eithe r Treatments 7 or 8. I t i s i n t e r e s t i n g to note, moreover, t h a t Treatments 7 and 8, which received no b r u i s i n g , d i d not r e s p i r e at the same ra t e , which i n d i c a t e s once more that f a c t o r s other than b r u i s i n g are more important i n t h e i r influence on r e s p i r a t i o n than b r u i s i n g i t s e l f . An i n t e r e s t i n g point i n connection with replacing f r u i t i n cold storage a f t e r a period at room temperature, i s the r a p i d i t y w i t h which r e s p i r a t i o n drops to the l e v e l at which i t stood before the f r u i t was removed from low temper-ature. This i s p a r t i c u l a r l y evident i n the case of the B a r t l e t t , Bosc and Winter N e l l s v a r i e t i e s . With Anjous the drop i n r e s p i r a t i o n i n t e n s i t y was more gradual and stopped at a l e v e l s l i g h t l y higher than the l e v e l i t stood at before - 41 -the pears were taken out o f s to rage . The f ac t t h a t pears w i l l respond so q u i c k l y to temperature change i s an important , c o n s i d e r a t i o n i n commercial movements o f f r u i t , e i t h e r from c o l d s torage to r i p e n i n g temperatures , or v i c e v e r s a . T h i s data would suggest a l s o that c o l d s torage i s an i d e a l method of a r r e s t i n g r i p e n i n g i n pears which have passed t h e i r c l i m a c t e r i c . Sugar Changes D u r i n g S torage and R i p e n i n g S ince r i p e n i n g o f f r u i t i s a r e s p i r a t i o n process i n v o l v i n g the o x i d a t i o n o f sugars to carbon d i o x i d e and water , i t i s i n t e r e s t i n g to know what changes take p l ace i n the sugar f r a c t i o n s o f pears dur ing s torage and r i p e n i n g . A number o f sugar analyses were made of the d i f f e r e n t v a r i e t i e s d u r i n g v a r i o u s stages between greenness and r i p e n e s s . The sugar ana lyses i n t h i s experiment were made by Lane and E n y o n ' s copper r e d u c t i o n method w i t h methylene blue as an i n t e r n a l I n d i c a t o r . In a d d i t i o n , the percentage o f s o l u b l e s o l i d s i n the j u i c e o f the pears was determined by means of a B r i x S p i n d l e . The r e s u l t s secured are g i v e n i n Table IV . I t i s i n t e r e s t i n g to note , f i r s t of a l l , t h e changes i n t o t a l sugars and sucrose a s s o c i a t e d w i t h r i p e n i n g . In the B a r t l e t t v a r i e t y , o n l y a t r a c e o f sucrose was found (.17%) when the f r u i t was ana ly sed a few days a f t e r be ing r e c e i v e d . As mentioned b e f o r e , however, t h i s v a r i e t y was i n a somewhat r i p e n e d c o n d i t i o n when i t a r r i v e d , and so t h i s f i r s t a n a l y s i s c o u l d not be c o n s i d e r e d as r e p r e s e n t i n g the sugar content o f green B a r t l e t t s . A f u r t h e r a n a l y s i s o f B a r t l e t t s , a f t e r - 42 -TABLE NO. IX  Sugar Changes During Storage and Ripening. Length Temper-V a r i e t y of Stor- ature of Condition age Storage of (days) (Deg.G.) F r u i t Soluble S o l i d s ( B r i x ing (Spindle) Sugar Redue- Sucrose T o t a l as Sugars Invert B a r t l e t t 30 0 ( 3 22 (30 0 (14 22 79 0 Bosc 19 0 41 0 (24 0 (15 22 Anjou 5 0 31 0 (7 0 (39 22 Winter 9 0 E e l i s ( 6 0 (18 22 Beginning 13.6 to turn yellow. Ripe 12.4 Ripe 11.2 Firm Green 15.4 Fi r m , S l i g h t 14.4 Tinge of yellow. Ripe 16.0 Firm Green 14 .6 Firm Green 14 .5 Ripe 13.4 Firm Green 15.8 Ripe 14 .6 9.50 .17 9.67 9.O3 .20 9.23 8.16 1.42 9.58 8.43 2 .55 IO .98 8.50 2.48 IO .98 10JL3 3.25 13.38 9.O3 1 .35 IO .38 8.36 I . 9 2 10.28 9.71 1.16 10.87 8.46 3.33 11.79 12.22 .47 12.69 _ 43 -they had been ripened at room temperature showed approximately the same amount of sucrose present (,20%), and a decrease i n t o t a l sugars from 9.67 to 9.23 percent. These data would suggest that some of the sugar had been l o s t i n the process of r e s p i r a t i o n . An i n t e r e s t i n g point i n connection with the B a r t l e t t v a r i e t y i s the f a c t that the t o t a l sugar content of pears ripened i n cold storage was higher than that of s i m i l a r pears ripened at room temperature, and also that a s u b s t a n t i a l amount of sucrose (1.42%1 was found i n the pears ripened i n storage. These data may be explained on the basis that c e r t a i n polysaccharide substances have been hydrolyzed to simple sugars, thus i n c r e a s i n g the sugar content of the pears f a s t e r t han sugar was being l o s t i n r e s p i r a t i o n . The sugar analyses of the Bosc v a r i e t y are of pa r t -i c u l a r i n t e r e s t since t h i s v a r i e t y shows a marked increase i n both reducing sugars and sucrose when ripened at room temper-ature, as compared with green f r u i t h e l d i n cold storage. Reducing sugar increased with ripe n i n g from 8.43 to 10.13 percent, and sucrose from 2.55 to 3 .25 percent., g i v i n g an increase i n t o t a l sugars from 10.98 to 13•38 percent. This high sugar content i n Boscs, p a r t i c u l a r l y sucrose, doubtless. accounts i n large measure f o r the excellent dessert q u a l i t i e s of t h i s v a r i e t y . The Anjou v a r i e t y shows r e l a t i v e l y l i t t l e change i n t o t a l sugars between a n a l y s i s j u s t a f t e r harvesting and a n a l y s i s when the pears are r i p e . In the second analyses of the f r u i t h e l d at 0°G. taken a month a f t e r the f i r s t analyses, - 44 -there was a s l i g h t change i n the reducing sugar-sucrose f r a c t i o n , some of the reducing sugar apparently being changed ,over into sucrose, since the t o t a l sugar content remained approximately the same. Upon r i p e n i n g the sucrose content dropped from I .92 to 1.16% and the reducing sugars increased from 8.36 to 9»71 percent, g i v i n g an increase i n t o t a l sugar from 10.28 to IO.87 percent. The Winter B e l i s v a r i e t y , analysed a few days a f t e r p i c k i n g showed the highest percentage of sucrose (3*33$) of any of the analyses reported. T o t a l sugar was also high (11.79$) 7 being the highest of a l l four v a r i e t i e s i n the i n i t i a l analyses. Upon r i p e n i n g , however, the sucrose content of Winter H e l i s dropped to .47 percent and the reducing sugar rose to I2.69 percent. This increase i n reducing sugar was much greater than could be accounted f o r by the loss i n sucrose, and probably was brought about by h y d r o l y s i s of s t a r c h , which the iodine t e s t showed to be present at the time of the f i r s t a n a l y s i s . I t i s i n t e r e s t i n g to note the consistent c o r r e l a t i o n throughout the t a b l e of the B r i x reading and the t o t a l sugar content of the j u i c e . In every a n a l y s i s made the B r i x reading of soluble s o l i d s on unripe f r u i t i s almost exactly 4 percent higher than the t o t a l sugar content of the j u i c e . This information would suggest that a r e l a t i v e l y accurate "quick method" of determining sugar content of unripe pears would be to take a B r i x Spindle percentage reading on the j u i c e and subtract 4. In the case of r i p e f r u i t , the B r i x Spindle - 4-5 -reading of solu b l e s o l i d s gave a f i g u r e between 2 and 3 percent higher than the a c t u a l t o t a l sugar content of the j u i c e . The data secured from these sugar t e s t s , however, seems to throw l i t t l e or no l i g h t upon what sugars are being broken down i n r e s p i r a t i o n . In every v a r i e t y , except B a r t l e t t , the t o t a l sugar content of the pears increased as the f r u i t ripened, the increase i n sugar being mainly i n the form of reducing sugars. This increase i n reducing sugars was con-s i d e r a b l y greater than could be accounted f o r by h y d r o l y s i s of the sucrose, and was probably due to h y d r o l y s i s of starch and c e r t a i n c e l l w a l l m a t e r i a l s . This data would i n d i c a t e , t h e r e f o r e , that l o s s of sugars i n r e s p i r a t i o n i s more than replaced by an increase i n sugars made a v a i l a b l e during r i p e n i n g . E f f e c t of B r u i s i n g on Sugar Changes and Loss of Weight In t h i s experiment an attempt was made to determine what changes occurred i n the sugar content of bruised and unbruised portions of the same pears s i x days a f t e r the b r u i s -ing treatment, had been given. The v a r i e t y used was Bosc. Bruised and unbruised portions from f i v e pears were chopped f i n e l y , and the sugar extracted from the t i s s u e by b o i l i n g i n a l c o h o l . An unbruised sample of pears was given s i m i l a r t r e a t -ment to act as a check. Reducing sugars and sucrose as i n v e r t were determined f o r the three samples. In addi t i o n a B r i x reading on the soluble s o l i d s of the j u i c e of bruised and unbruised pears was taken. A 30 gram sample of the bruised and unbruised t i s s u e and of the check f r u i t was dried i n the oven f o r 4-8 hours at 90° C. and 24 hours at 100° C. to determine - 4 6 -the dry matter content of the d i f f e r e n t samples, The data secured are presented i n Tables X (a) end X (b). TABLE X (a) Amount of Sugar by A l c o h o l E x t r a c t i o n i n 3° Grams Green Tissue of Bruised and Unbruised Bosc Pears, Expressed i n Percentage of Green Weight and Dry Weight. Sugars i n % of Green Wt. Sucrose Dry Weight Total % Sugar Treatment Re due- as of Tissue Sugar of Dry in g Invert T o t a l (Grams) (grms) Weight Bruised Pears Bruised P o r t i o n Unbruised P o r t i o n 7.12 6.68 2.95 2.68 10.07 9.36 5.4-6 3.021 55.3 4 . 6 6 2.808 60.2 Check 6.65 2.66 9.31 4 . 8 3 2.793 57.8 TABLE X (b) Treatment B r i x Spindle Soluble S o l i d s %. Reducing Sucrose Total as Invert Unbruised Tissue of Bruised pears. 12.8 8.50 2.98 1 1 . 4 8 Check 13.2 9.07 2.79 11.86 Loss of weight i n grams of above pears during the s i x days between b r u i s i n g and a n a l y s i s . Weight Before B r u i s i n g - 987.5 Check before - 1005*3 A f t e r 6 days - 966.5 A f t e r 6 days - 998.5 Loss % - 2.18 Loss % - .7 - 47 -These r e s u l t s i n d i c a t e that b r u i s i n g b r i n g s about a h i g h e r c o n c e n t r a t i o n o f sugars i n the b r u i s e d than i n the u n b r u i s e d p o r t i o n of the f r u i t , and a l so that the sugar con-tent o f the u n b r u i s e d p o r t i o n o f b r u i s e d pears i s p r a c t i c a l l y i d e n t i c a l w i t h that o f the b r u i s e d p o r t i o n . The r e l a t i v e p r o p o r t i o n s o f sucrose and r e d u c i n g sugars i n the b r u i s e d and unbru i sed p o r t i o n s of the f r u i t s remained the same. I t i s s i g n i f i c a n t to n o t e , however, that the b r u i s e d f r u i t d u r i n g the 6 days between b r u i s i n g and a n a l y s i s l o s t 2.18% i n w e i g h t , w h i l e unbru i sed f r u i t l o s t o n l y .7%. I t i s a l t o g e t h e r p r o b a b l e , t h e r e f o r e , that a l a rge p o r t i o n of the l o s s i n weight i n the b r u i s e d f r u i t was due to evapora t ion of water from the b r u i s e d t i s s u e , thereby r e s u l t i n g i n a h i g h e r c o n c e n t r a t i o n of sugars i n the i n j u r e d p a r t , as shown i n Table X ( a ) . Examina t ion of the b r u i s e d t i s s u e i n these Bosc pears showed a d r y , loose c o n s i s t e n c y of the t i s s u e , suggest ing s t r o n g l y t h a t a l o s s o f water had occurred from the i n j u r e d p o r t i o n . The dry weights o f 30 gram p o r t i o n s o f b r u i s e d and u n b r u i s e d t i s s u e from the same pears were 5*46 and 4.66 grams r e s p e c t i v e l y , w h i l e the dry weight of 30 grams of t i s s u e from the check f r u i t was 4 .83 grams, approximate ly the same as the dry weight o f the unbru i sed p o r t i o n s of b r u i s e d f r u i t . The d i f f e r e n c e , however, between the b r u i s e d and unbrui sed p o r t i o n o f the same f r u i t i s (5.46 and 4.66 grams^great enough to appear q u i t e s i g n i f i c a n t . T h i s g r e a t e r dry weight of the b r u i s e d - 48 -p o r t i o n aga in suggests that the i n j u r e d t i s s u e had l o s t water . When the t o t a l sugars were c a l c u l a t e d back to a percentage of the dry we ight , i t was found tha t the percentage of sugars was, 55.3 > 60.2 and 57.8 f o r the b r u i s e d , unbrui sed and check t i s s u e r e s p e c t i v e l y . I f there had been no other e f f e c t but l o s s o f water from b r u i s e d t i s s u e , i t might be expected t h a t sugars would comprise the same percentage of dry weight i n both b r u i s e d and unbru i sed samples. I t might a l so appear tha t the lower percentage o f sugar i n the b r u i s e d t i s s u e was caused by a l o s s of sugar i n r e s p i r a t i o n , but r e s p i r a t i o n da ta presented elsewhere, do not bear t h i s o u t . In v iew of the f a c t that there was a v a r i a t i o n i n percent of sugar of dry weight between the check sample and the u n b r u i s e d sample o f 57•8 and 60.2%, i t i s q u i t e p o s s i b l e tha t an e r r o r o f sampling might have o c c u r r e d i n the bru i sed sample, b r i n g i n g the percentage sugars t h e r e , down to 55 s3$« I t would be o f va lue to check t h i s p o i n t a g a i n . The da ta i n Table X (b ) , showing the percentage o f sugars and s o l u b l e s o l i d s i n the expressed j u i c e from the same pears as used i n Table X (a) show a s l i g h t v a r i a t i o n i n r e l a t i v e percentages of sugar from unbru i sed t i s s u e of b r u i s e d pears and check f r u i t . M i c r o s c o p i c a l E x a m i n a t i o n - o f B r u i s e d T i s sue S e c t i o n s cut through pears , i n c l u d i n g both b r u i s e d and unbru i sed t i s s u e , showed a d i s t i n c t l i n e o f demarcation between the i n j u r e d and l i v i n g c e l l s . A p p a r e n t l y a c o r k - l i k e l a y e r had been l a i d down by the normal c e l l s surrounding the i n j u r e d ones, which wa l l ed o f f the b r u i s e d p o r t i o n complete ly - 49 -from the l i v i n g t i s s u e , thus p r e v e n t i n g the evapora t ion o f water from the h e a l t h y t i s s u e and p r e v e n t i n g the spread of the b r u i s e d a r e a . 'The c e l l s i n the b r u i s e d t i s s u e were d i s o r g a n i z e d rup tured and c o l l a p s e d , the t i s s u e i t s e l f be ing brown and tough. The f a c t t h a t t h i s cork l a y e r i s l a i d down between t h e b r u i s e d and normal t i s s u e e x p l a i n s i n a l a rge degree why l o s s o f weight from b r u i s e d pears i s not e x c e s s i v e , and r i p e n i n g and r e s p i r a t i o n are not a c c e l e r a t e d to any a p p r e c i a b l e ex tent . S o f t e n i n g o f F r u i t D u r i n g Storage One o f the important methods of measuring r a te of r i p e n i n g o f s torage pears i s by means o f the pressure t e s t e r . The pres sure t e s t e r i n d i c a t e s the force r e q u i r e d to press a b l u n t , rounded p l u n g e r , of g i v e n diameter , a g iven depth i n t o the f r u i t . The t e s t i s based on the f a c t that the sof tness of the f l e s h i n c r e a s e s as the f r u i t r i p e n s . P r e s s u r e t e s t s were made on samples of pears h e l d i n c o l d s torage a t i n t e r v a l s d u r i n g the experiment . The f r u i t was a l lowed 12 hours to warm up i n room temperature , before the t e s t was t a k e n . The data secured are presented i n Table X I . TABLE NO. X I . ' 0 S o f t e n i n g o f Pears D u r i n g Storage at 0 C. Date Pressure i n Pounds. V a r i e t y P i c k e d __ O c t . ' 12. "Nov . 1 Nov. 21 B a r t l e t t Aug . 29 14.7 6 .2 3.0 Ripe Bosc Sep t . 21 14.2 14.1 I3.O Anjou O c t . 5 13.2 13.5 H « 6 Winter N e l i s O c t . 26 - l g . 14.5 - 50 -The B a r t l e t t s were the o n l y v a r i e t y which r ipened comple te ly under c o l d s torage c o n d i t i o n s . The Bosc,: Anjou and Winter H e l i s v a r i e t i e s showed on ly a s l i g h t degree o f s o f t e n i n g d u r i n g the p e r i o d they were h e l d at 0 ° C . Pres sure Tes t , o f .Experimental F r u i t at E n d ' o f Storage P e r i o d As a f u r t h e r check upon the e f f e c t o f b r u i s i n g upon r a t e of r i p e n i n g , pres sure t e s t s were taken of the Anjou# and Bosc v a r i e t i e s at the end of the experiment . These data are found i n Tab le X l l . The data i n t h i s t a b l e show very l i t t l e v a r i a t i o n i n so f tness i n r e l a t i o n to the d i f f e r e n t t rea tments . TABLE NO. X I I Pre s sure T e s t s o f C o l d Storage Pears Subjected to D i f f e r e n t Treatments at the End of the Storage P e r i o d * V a r i e t y Length of Pres sure i n Pounds f o r Treatments Number Storage . (days) 4 5 6 7 8 9 Anjou 51 14.0 13.5 13.2 4.1 3.8 4.7 Bosc 46 12.8 I3.9 13.1 5.0 5.0 5.1 H e l d throughout the experiment at 0° C . Treatment 4 - B r u i s e d at s t a r t . Treatment 5 ~ U n b r u i s e d . Treatment 6 - B r u i s e d a f t e r 2 to 3 weeks. H e l d at 0 ° C . w i t h i n t e r v a l s o f room temperature . Treatment 7 " U n b r u i s e d . Treatment 8 - B r u i s e d a f t e r 2 to 3 weeks. Treatment 9 - B r u i s e d at s t a r t . -•51 -With the An jou v a r i e t y , f r u i t o f Treatment 4 which was b r u i s e d when the f r u i t was p l a c e d i n s torage shows a h i g h e r pressure r e a d i n g than u n b r u i s e d f r u i t , o r f r u i t r e c e i v i n g delayed b r u i s i n g , whereas i n the Bosc v a r i e t y the unbru i sed f r u i t gave the h i g h e s t p re s sure r e a d i n g . These v a r i a t i o n s , however, are no l a r g e r than n o r m a l l y occur i n d u p l i c a t e samples of commercial f r u i t . . The p re s sure read ings o f Treatments 7t 8 and 9 i n d i c a t e t h a t removal o f - t h e pears on two occas ions to room temperature f o r a few days have r e s u l t e d i n almost complete r i p e n i n g o f the f r u i t , the Anjous showing a pre s sure of 4 pounds, and the Boscs 5 pounds. A pre s sure o f 3 pounds i s c h a r a c t e r i s t i c of r i p e f r u i t . L i k e w i s e i n these f i g u r e s there seems to be no s i g -n i f i c a n t v a r i a t i o n a t t r i b u t a b l e to b r u i s i n g t reatment . Appearance o f the F r u i t at the End o f the Experiments At the end of the experiments the f r u i t was removed from the r e s p i r a t i o n c o n t a i n e r s and examined f o r any v i s i b l e d i f f e r e n c e s which might be ev ident as a r e s u l t o f b r u i s i n g t rea tment . F r u i t of Treatments 1, 2 and 3 h e l d at room temper-a t u r e , a l l r i p e n e d at e x a c t l y the same t ime, as f a r as cou ld be determined wi thout a c t u a l l y pres sure t e s t i n g the pear s . In the case o f Treatments 4, 5 and 6 , h e l d at 0 ° G . there was no apparent d i f f e r e n c e i n the c o n d i t i o n o f the three l o t s of p e a r s . Any y e l l o w i n g i n the f r u i t , such as occurred i n the B a r t l e t t and Bosc v a r i e t i e s , e x i s t e d to a uni form degree i n a l l three samples . L i k e w i s e i n Treatments 7 , 8 and 9 , the f r u i t showed no outward d i f f e r e n c e s as a r e s u l t o f b r u i s i n g t reatment . In the case of a l l the b r u i s i n g treatments a p p l i e d , where - 52 - . minute ruptures i n the s k i n had occurred, , there was a g rea ter tendency f o r mould i n f e c t i o n s to set i n , than i n f r u i t wi th i t s s k i n i n t a c t . Mould growth i n c o l d storage occur red only on B a r t l e t t pear s , and seemed to "be a s s o c i a t e d w i t h almost complete r i p e n e s s . A f t e r moulds had set i n , r e s p i r a t i o n measurements were d i s c o n t i n u e d . Moulds occurred on room temperature f r u i t o n l y a f t e r the f r u i t had passed i t s best p e r i o d o f r i p e n e s s . Loss o f Weight o f Pears Dur ing Progres s of t h e Experiments The weights o f the v a r i o u s l o t s of f r u i t were determined before the f r u i t was p l a c e d i n r e s p i r a t i o n con-t a i n e r s and a f t e r t h e end of the r e s p i r a t i o n measurements. The da ta are found i n Table X I I I . TABLE! X I I I . I n f l u e n c e of V a r i o u s Treatments on Loss of Weight o f Pears  D u r i n g S to rage . Weight i n Grams. T r e a t -ment B a r t l e t t Bosc An.iou Winter N e l l s N.O a Before A f t e r Before A f t e r Before A f t e r Before tAf te r 1 675 662 1105 IO96 1083 1067 1075 1065 2 684 675 1072 1 0 6 4 1086 1076 1016 1010 3 1166 1159 1026 1014 977 969 4 1032 1020 1002 1000 1092 1091 1047 1042 5 1063 1053 1066 1060 1019 1017 975 970 6 956 947 953 949 991 986 1071 1065 7 906 879 1048 1009 976 961 1029 1026 8 965 947 1060 1009 1048 I O 3 6 1038 1031 9 920 901 1066 1012 1030 1020 1042 1029 Days i n , 25 Storage 44 46 !?i ^ - 53 -There appears to he only one s i g n i f i c a n t f a c t about t h i s t a b l e , namely that no a p p r e c i a b l e d i f f e r e n c e s i n l o s s e s o f weight have o c c u r r e d d u r i n g the s torage p e r i o d i n pears r i p e n e d at room temperature , or h e l d throughout the experiments i n c o l d s t o r a g e . The probable e x p l a n a t i o n f o r t h i s i s the f a c t tha t a s a t u r a t e d atmosphere was mainta ined at a l l times w i t h i n the r e s p i r a t i o n c o n t a i n e r s , due to the water g iven o f f i n r e s p i r a t i o n . Drops of water cou ld always be found on the i n s i d e of the c o n t a i n e r s , i n d i c a t i n g tha t the s a t u r a t i o n po in t had been r e a c h e d . Under such c o n d i t i o n s , pears , or any other k i n d s o f f r u i t , a r e not l i k e l y to l o se as much water as would be l o s t by the same f r u i t h e l d under c o n d i t i o n s of atmosphere h u m i d i t y . The v a r i a t i o n s i n l o s s o f weight i n the d i f f e r e n t samples can probab ly be a t t r i b u t e d to i n d i v i d u a l i t y o f the pears themselves . DISCUSSION AND CONCLUSIONS The da ta presented i n t h i s r epor t would seem to i n d i c a t e one main t h i n g , and that i s , tha t b r u i s i n g i n j u r y does not a p p r e c i a b l y a f f e c t e i t h e r the r e s p i r a t i o n or the s torage q u a l i t i e s o f pear s . In a l l the data secured , f a c t o r s o ther than b r u i s i n g treatment seemed to i n f l u e n c e r e s p i r a t i o n more than the b r u i s i n g i t s e l f . From the evidence presented , i t would appear t h a t pears are c h a r a c t e r i z e d by a tremendous amount of v a r i a b i l i t y , which expresses i t s e l f among other ways, i n a p e r i o d i c i t y of a c t i v i t y i n the r e s p i r a t i o n mechanism of the f r u i t . Based on the work of K i d d and West on the i n d i v i d u a l i t y o f d i f f e r e n t apples i n an apparent ly = 54 -uni form sample, i t would seem reasonable to po s tu l a t e that t h i s same i n d i v i d u a l i t y would e x i s t i n p e a r s . K i d d and West found that the r e s p i r a t i o n trends of d i f f e r e n t i n d i v i d u a l apples d i f f e r e d markedly f rom each o t h e r , some f r u i t s being low and some h i g h r e s p i r a t i o n i n d i v i d u a l s . In exper imenta l samples of pears o f f i v e to e ight i n d i v i d u a l s , such as were used i n t h i s work, i t would be q u i t e reasonable to assume that v a r y i n g p r o p o r t i o n s of low and h i g h r e s p i r a t i o n i n d i v -i d u a l s i n a sample might be the cause of the v a r i a b i l i t y o c c u r r i n g i n the samples o f f r u i t used . Thus,- where a sma l l number o f pears are used i n a sample, the odds would be q u i t e f a v o r a b l e toward a random sample o f f r u i t c o n t a i n i n g main ly low or m a i n l y h i g h r e s p i r a t i o n . i n d i v i d u a l s . Such an assumption might e x p l a i n s a t i s f a c t o r i l y why c e r t a i n l o t s of f r u i t showed h i g h e r r e s p i r a t i o n t rends than others throughout the whole course of the experiment, i r r e s p e c t i v e o f t reatment . Th i s would not n e c e s s a r i l y e x p l a i n , however, the p e r i o d i c i t y , i n r e s p i r a t i o n e x h i b i t e d by a l l the samples. The apparent s e n s i t i v i t y of pears to change of c o n d i t i o n s , as expressed by t h e i r c a t a c l y s m i c r e s p i r a t i o n response to change o f temperature, would suggest a l so t h a t o t h e r , l e s s e a s i l y s t u d i e d , c o n d i t i o n s w i t h i n the f r u i t i t s e l f might be r e s p o n s i b l e i n par t f o r v a r i a t i o n i n r e s p i r a t o r y b e h a v i o r . The data showing the sugar analyses and dry weight d e t e r m i n a t i o n s of b r u i s e d and unbrui sed pear t i s s u e would appear to be p a r t i c u l a r l y s i g n i f i c a n t i n that they suggest - 55 -tha t b r u i s i n g i n j u r y to pears r e s u l t s ma in ly i n a l o s s o f water from the i n j u r e d p a r t , w i t h no apparent change i n sugar content i n the r e s t of the pear . The f a c t tha t b r u i s i n g i n j u r y does not a f f e c t the r e s p i r a t i o n i n t e n s i t y of pears would seem to be accounted f o r by the f a c t a c o r k - l i k e l a y e r forms between the i n j u r e d and h e a l t h y t i s s u e , prevent ing the spread o f the b r u i s i n g i n j u r y , and l o s s o f water from the r e s t of the f r u i t . Th i s c o r k - l i k e l a y e r would appear to i s o l a t e the b r u i s e d p o r t i o n of the f r u i t from the h e a l t h y t i s s u e * From the pres sure t est data , and the s i m i l a r appearance of b r u i s e d and unbru i sed f r u i t at the t e r m i n a t i o n of the experiment , the evidence would f u r t h e r i n d i c a t e that b r u i s i n g i n j u r y has l i t t l e e f f e c t upon the keeping q u a l i t i e s of p e a r s . The data secured on the e f f ec t o f change i n temper-a ture upon r e s p i r a t i o n i n t e n s i t y i n pear s , a r e p a r t i c u l a r l y s i g n i f i c a n t i n tha t they demonstrate the n e c e s s i t y o f s h i p p i n g pears i n r e f r i g e r a t e d car s where they are to be moved from c o l d s torage at one p o i n t to another . In s e v e r a l ins tances the r e s p i r a t i o n r a t e of the f r u i t i n c r e a s e d 10 to l g times w i t h an i n c r e a s e i n temperature from 0° to 20° C. The r e s p i r a t i o n i n t e n s i t y o f f r u i t s to red at 0°C. and f r u i t h e l d c o n t i n u o u s l y at room temperature, demonstrates c l e a r l y the r e t a r d i n g e f f e c t c o l d storage has upon r i p e n i n g . Sugar changes i n f r u i t between p i c k i n g and r i p e n i n g are i n t e r e s t i n g , s i n c e they i n d i c a t e the d i f f e r e n c e between - 56 -v a r i e t i e s i n p r o p o r t i o n s of r e d u c i n g sugar and sucrose , and the changes i n these f r a c t i o n s a s s o c i a t e d w i t h r i p e n i n g . The f a c t t h a t Bosc has a h i g h sucrose content when r i p e probab ly accounts f o r the s u p e r l a t i v e q u a l i t y of t h i s v a r i e t y , w h i l e the low sucrose content of B a r t l e t t probably exp la ins i t s lower r e l a t i v e q u a l i t y . That r e s p i r a t i o n lo s se s do not reduce the amount of sugars present i n r i p e pears i s i n d i c a t e d by the f ac t tha t t o t a l sugar content of three out of the four v a r i e t i e s i n c r e a s e d markedly . The c o n c e n t r a t i o n of carbon d i o x i d e necessary to depress r e s p i r a t i o n i n the v a r i e t i e s s t u d i e d throws an i n t e r e s t i n g l i g h t upon the percentage of t h i s gas which would l i k e l y be d e s i r a b l e f o r h o l d i n g pears i n gas s to rage . S i n c e the main emphasis o f t h i s work has been l a i d upon the e f f e c t o f b r u i s i n g upon keeping q u a l i t i e s of pears , i t would seem wise to c a u t i o n that a l though b r u i s i n g i n j u r y does not appear to inc rea se r e s p i r a t i o n and r i p e n i n g , the f r u i t shou ld s t i l l be handled c a r e f u l l y . Pears which a r e handled so roughly t h a t a c t u a l l a c e r a t i o n s i n the f l e s h occur , are l i a b l e to develop "nest r o t s " i n the f r u i t package which spread and o f ten comple te ly r u i n a whole box o f pear s . Pears should be handled as c a r e f u l l y as p o s s i b l e at a l l t imes , s ince b r u i s i n g , even i f i t does not permit i n f e c t i o n by r o t s , d e t r a c t s from the appearance o f the f r u i t and lowers the r e t u r n s secured by the grower. - 57 -SUMMARY I n i t i a l and de layed b r u i s i n g treatment was g iven to B a r t l e t t , Bosc , A n j o u and Winter H e l l s pears h e l d at room temperature , i n 0 ° C . s torage , and f r u i t which was moved from one temperature to the o t h e r . B r u i s e d f r u i t was compared w i t h u n b r u i s e d f r u i t as a check. Pears r i p e n e d at room temperature d i d not-show any s i g -n i f i c a n t response i n r a t e o f r e s p i r a t i o n to b r u i s i n g t rea tment , F a c t o r s other than b r u i s i n g treatment appeared to i n f l u e n c e r e s p i r a t i o n i n t e n s i t y to a much g r e a t e r degree than b r u i s i n g i t s e l f . R e s p i r a t i o n i n t e n s i t y o f a l l v a r i e t i e s f l u c t u a t e d w i d e l y from day to day, the f r u i t appear ing to r e s p i r e i n waves. No s i g n i f i c a n t d i f f e r e n c e could be de tec ted i n ra te of r e s p i r a t i o n o f b r u i s e d , cut and unbru i sed f r u i t . R e s p i r a t i o n curves f o r d i f f e r e n t v a r i e t i e s r ipened at room temperature d i f f e r e d markedly . Winter N e l i s r e s p i r e d at a r a p i d l y i n c r e a s i n g r a t e , both before and a f t e r . r i p e n i n g . Bosc r e s p i r e d i n t e n s e l y u n t i l r i p e and then f e l l o f f r a p i d l y . Anjou r e s p i r e d at a s lowly i n c r e a s i n g r a t e and took twice as long to reach r ipenes s as the o ther two v a r i e t i e s . Carbon d i o x i d e accumulat ion i n r e s p i r a t i o n c o n t a i n e r s , where the l e n g t h o f the r e s p i r a t i o n p e r i o d was g r e a t e r than 24 h o u r s , almost complete ly depressed p r o d u c t i o n of carbon d i o x i d e . The percentage of carbon d iox ide - 58 -(6) nece s sa ry to depress r e s p i r a t i o n was 7 percent f o r An jou , 12 percent f o r Bosc and 14 percent for Winter H e l l s . ,(7) T h e ra te o f r e s p i r a t i o n o f b r u i s e d and unbru i sed -pears h e l d c o n t i n u o u s l y i n s torage at 0 ° C . , d i d not show any s i g -n i f i c a n t d i f f e r e n c e , w i t h the p o s s i b l e except ion of a s l i g h t r i s e f o l l o w i n g delayed b r u i s i n g w i t h the Winter H e l i s v a r i e t y . (8) Removal o f f r u i t from 0 ° C . to room temperature caused immediate and intense a c t i v a t i o n o f r e s p i r a t i o n , when the f r u i t was r e t u r n e d to 0 ° C . , r e s p i r a t i o n dropped as f a s t as i t had r i s e n i n a l l v a r i e t i e s except A n j o u . Removal of pears a second time to room temperature r e s u l t e d i n a s t i l l g r e a t e r r e s p i r a t i o n i n t e n s i t y . (9) V a r i a t i o n o c c u r r e d i n r e s p i r a t i o n r a te s of d i f f e r e n t l o t s of f r u i t removed to room temperature from 0 ° C . , but these v a r i a t i o n s were not c o n s i s t e n t l y c o r r e l a t e d wi th b r u i s i n g t rea tment . (10) Sugar ana lyses o f pears s t o r e d at 0 ° C . and f r u i t r ipened at room temperature r e v e a l e d t h a t wi th the except ion of the B a r t l e t t v a r i e t y , an increa se i n t o t a l sugars accompanied r i p e n i n g . T h i s was most marked w i t h t h e Bosc and Winter H e l i s v a r i e t i e s . A l l v a r i e t i e s , except B a r t l e t t , showed an i n c r e a s e i n reduc ing sugars dur ing r i p e n i n g , w h i l e Bosc showed a l s o an increa se i n sucrose . Sucrose d e c l i n e d upon r i p e n i n g w i t h the Winter H e l i s v a r i e t y , but remained n e a r l y the same w i t h the Anjou v a r i e t y . (11) Ana ly se s made of b r u i s e d and unbruised p o r t i o n s of Bosc pear s , showed a s l i g h t increase i n percentage o f sugars i n the b r u i s e d p o r t i o n , whi le the unbrui sed p o r t i o n con-t a i n e d the same amount o f sugar as normal unbruised f r u i t . The d r i e d - o u t appearance of b r u i s e d t i s s u e , coupled w i t h the f a c t tha t b r u i s e d pears l o s t between two and three t imes as much weight as unbrui sed f r u i t , suggests that the on ly e f f e c t o f b r u i s i n g upon pears i s a l o s s of v/ater from the b r u i s e d p a r t . (12) M i c r o s c o p i c a l examinat ion of contiguous b r u i s e d and unbru i sed t i s s u e , r evea l ed a d i s t i n c t l i n e of demarcation between i n j u r e d and h e a l t h y c e l l s , due to format ion of . a c o r k - l i k e l a y e r . (13) Pre s sure t e s t readings taken at i n t e r v a l s dur ing storage r e v e a l e d a s l i g h t amount o f s o f t e n i n g i n Bosc , Anjou and . Winter E e l i s and complete r i p e n i n g of the B a r t l e t t v a r i e t y . (14) Pres sure t e s t read ings taken on b r u i s e d and unbru i sed exper imenta l pears at the end of the t e s t , r evea led no s i g n i f i c a n t d i f f e r e n c e s i n degree o f hardness . (15) B r u i s e d and unbru i sed pears r i p e n e d s imul taneous ly at room temperature . Those l o t s o f f r u i t h e l d at 0 ° C . were a l so o f i d e n t i c a l outward appearance at the end o f the exper iment . (16) There was no a p p r e c i a b l e d i f f e r e n c e between l o s s o f weight d u r i n g the experiment, o f b r u i s e d and unbrui sed f r u i t h e l d at e i t h e r 0 ° C . or at room temperature . Thi s - 60 -(16) was probab ly due to the s a tura ted c o n d i t i o n of the atmosphere w i t h i n the r e s p i r a t i o n c o n t a i n e r s . - 61 -LITERATURE CITED 1. B ige low, D , , H . C. Gore , and B. J . Howard. S tud ie s on A p p l e s . Par t 1. Storage R e s p i r a t i o n and Growth. U . S . D . A . B u r . Chem. B u i . 94, I965. 2. B l a s d a l e , ¥ . C . , P r i n c i p l e s of Quant i t a t i ve A n a l y s i s , p . p . 309 - 310, D . Van Udstrand Company, 1924. 3. Browne, C. A . A Chemical Study o f the Apple and i t s P r o d u c t s . Penn. D e p t . o f A g r i c , B u i . 58,1894. 4. Burroughs , A . M . Changes i n the R e s p i r a t i o n Rate of R i p e n i n g A p p l e s . P r o c . Am. Soc . H o r t . S c i . , V o l . 19, 1922. 5. Ewert , D i e K o r r e l a t i v e n E i n f l u s s e des Kerns Beim R e i f e p r o z e s s der P r u c h t e . In Landw J a h r b . , Bd . 39, Heft 3, 1910. 6. P i s h e r , D. V . Pear H a r v e s t i n g and Storage I n v e s t i g a t i o n s . Rept . o f Experiments Conducted at Summerland E x p e r i m e n t a l S t a t i o n , 1934. 7. Gerhard t , P . and B . D . E z e l l . Sugar and A c i d i t y Changes i n Pears as In f luenced by V a r i e t y and M a t u r i t y . P r o c Am. S o c H o r t . S c i . , V o l . 32> 1934. 8 . Gore , H . C . S tud ie s on P r u i t R e s p i r a t i o n . U . S . D . A . B u r . Chem. B u i . 142, 1911. 9. K i d d , P . , and G. West . Report of Pood I n v e s t i g a t i o n Board , p . 34. H i s M a j e s t y ' s S t a t i o n e r y O f f i c e , London, 1924. 10. Report of Pood I n v e s t i g a t i o n Board , pp . 121 - 123. H i s M a j e s t y ' s S t a t i o n e r y O f f i c e , London, 1929. 11. Lane, J . H . and L . Enyon . Determina t ion o f Reducing Sugars by Means o f P e h l i n g ' s S o l u t i o n w i t h Methylene Blue as I n t e r n a l I n d i c a t o r . J our . Soc . Chem. Ind . 42, 1923. 12. Lewi s , C . I . , J . R. Magness, and C . C. Gate . P r e l i m i n a r y Re-oort o f Pear H a r v e s t i n g I n v e s t i g a t i o n s i n Rogue R i v e r V a l l e y , Oreg . A g r . Exp . S t a . , B u i . 154, 1918. 13. Magness, J . R. I n v e s t i g a t i o n s i n the R i p e n i n g and Storage o f B a r t l e t t Pears , J o u r . A g r i c R e s . , V o l . 19, Ho. 10, 1920. - 62 -14. Magness, J . R . , and W. S. B a l l a r d . The R e s p i r a t i o n o f B a r t l e t t P e a r s . J our . A g r i c . Res . V o l . 32, No. 9, 1926. l g . Magness, J . R . , and A . M . Burroughs . Second Report , S tud ie s i n Apple S torage , Marble Labora tory I n c . , Canton, P a . , I92I-I922. 16. Magness, J . R . , and H . C , D i e h l . P h y s i o l o g i c a l S tudies on Apples i n S to rage . Jour . A g r i c . Res . V o l . 27, 1924. 17. Osborne, C D . , F a c t o r s A f f e c t i n g the Storage Q u a l i t i e s o f Apples w i t h S p e c i a l Reference to R e s p i r a t i o n . B a c h e l o r ' s T h e s i s , Dept . o f H o r t i c u l t u r e , U n i v e r s i t y o f B r i t i s h Columbia , I933. 18. Tha tcher , R. W. Enzymes o f Apple s and T h e i r R e l a t i o n to the R i p e n i n g P r o c e s s . J o u r . A g r i c . Res . V o l . 5» 1915. 19. Thompson, P . , and A . C . W h i t t i e r . Forms o f Sugar Found i n Common F r u i t s . P r o c . Am. Soc . H o r t . S c i . , vol. 9, 1913. 20. W i n k l e r , C , and G, Lunge. Handbook of T e c h n i c a l Gas A n a l y s i s , John Van V o o r s t , 1 Pa te rnos te r Row, London, 1885* - 63 -AQKHGWEETJGlEIfT The w r i t e r wishes to express h i s s i n c e r e a p p r e c i a t i o n to D r . G. H . H a r r i s f o r the many suggest ions he has g i v e n and the constant i n t e r e s t he has shown through-out the progress o f the work. Thanks are a l so due to M r . R. C, Palmer, Super intendent o f the Dominion Exper imenta l S t a t i o n , Summerland, f o r h i s k i n d c o - o p e r a t i o n i n supp ly ing the f r u i t r e q u i r e d fo r the p r o j e c t . A p p r e c i a t i o n i s a l so expressed to M r . M a r t i n and s t a f f , o f the Vancouver Ice and Gold Storage Company, for the f a c i l i t i e s and s e r v i c e s t h a t have been extended i n the work c a r r i e d out under c o l d s torage temperature . 

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