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Cytological investigations of the genus Alaria greville : as it occurs on the West Coast of North America Robinson, Gordon George Christopher

Abstract

Although the taxonomy of the brown algal genus Alaria Greville of the order Laminariales has recently been elucidated, neither the morphological nor the cytological aspects of the life-cycles of the species occurring on the west coast of North America has been investigated. Therefore a major part of this present project has been to establish the morphological and cytological phases of several species of Alaria. Since the earliest investigations into the cytology of the Laminariales the concepts of the nuclear division processes have not changed as they have in higher organisms. A supplementary objective has therefore been the application of modern techniques and interpretations to nuclear divisions in the genus Alaria. During 1964-1967 samples of Alaria marginata Postels et Ruprecht, Alaria nana Schrader, Alaria tenuifolia Setchell, Alaria taeniata Kjellman, Alaria fistulosa Postels et Ruprecht and Alaria grandifolia J. Agardh were collected from the west coast of North America, from Cape St. Elias, Alaska to Pescadero Point, California. Cultures of these species were established from spore suspensions and maintained under controlled conditions until young sporophytes were produced. From these cultures it has been demonstrated that the life-cycles of all six species show an alternation of heteromorphic generations: macroscopic sporophytic and microscopic dioecious gametophytic generations. It has also been established that there is a corresponding chromosomal alternation of generations, the sporophyte being diploid and the gametophyte, haploid. The development of male and female gametophytes, the production of gametangia, fertilisation, and the early developmental stages of the young sporophytes have been examined. The similarities and differences between these phases in Alaria and other members of the Laminariales have been investigated and found to be similar except for the germination of zoospores of A. marginata, the formation of the egg cells in all the Alaria spp. and the occurrence of a possible "fertilisation pore" and "tube" in the eggs of A. taeniata. The occurrence of parthenogenesis and the production of malformed haploid "parthenosporophytes" are reported. Meiosis in the immature zoosporangia and mitosis in gametophytes and young sporophytes have been observed, compared with these processes in other members of the Laminariales, and found to be similar in a number of cases. However, the concepts of meiosis held by many earlier authors are not applicable to this process in Alaria. A haploid chromosome number of approximately 14 alternates with a diploid number of approximately 28 in A. marginata, A. nana, A. tenuifolia, A. fistulosa and A. taeniata. The haploid number of A. grandifolia is approximately 24. Consequently only A. grandifolia can possibly be distinguished on the basis of chromosome numbers. The methods used in laminarian cytology and the difficulties involved in counting the extremely small chromosomes of the members of this order have been critically discussed.

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