BRIEFER ARTICLES 



A NOTE ON THE GENERATIONS OF POLYSIPHONIA' 



(with one figure) 



Yamanouchi 2 concludes from his cytological work on Polysiphonia 

 violacea that "there is an alternation of a sexual plant (gametophyte) and 

 an asexual plant (sporophyte) in the life history of Polysiphonia, the 

 cystocarp being included as an early part of the sporophytic phase." 

 He found that on the cystocarpic plants there was an occasional ab- 

 normality "in the form of a cell resembling a monospore, but having 

 the same cell lineage as the tetraspore mother cell." He traced the 

 development of these cells and found that although cleavage furrows 

 appeared, the nucleus rarely entered a mitosis and the cell never divided. 

 He makes note of the fact that Lotsy has found tetraspores on the same 

 plants with sexual organs in Chylocladia kaliformis and that Davis has 

 found the same condition in Spermatothamnion Turneri, Ceramiutn 

 rubrum, and C allithamnion Baileyi. He suggests that possibly the 

 structures reported as tetraspores are really monospores and are de- 

 veloped with a suppression of reduction phenomena, or that the sexual 

 organs are developed apogamously. 



Lewis 3 has attempted an experimental test of the truth of Yama- 

 nouchi's conclusion. He says: "Cytological observations on Poly- 

 siphonia by Yamanouchi, on Griffithsia by myself, and on Delesseria 

 by Svedelius render it probable that in these genera at least, and pre- 

 sumably in all Florideae in which tetraspores and sexual organs are borne 

 on separate individuals, there exists an alternation of sexual and asexual 

 plants, the carpospores giving rise on germination to asexual, and the 

 tetraspores to sexual individuals." The results that he obtained by 

 growing plants from the spores of Polysiphonia violacea, Griffithsia 

 Bornctiana, and Dasya elegans are consistent with the above theory, no 

 carpospores having been found to produce sexual individuals, and no 

 tetraspores to produce asexual individuals. Both the cytological and 

 the experimental evidence would thus seem to unite in indicating that 



1 Contributions from the Puget Sound Marine Station, no. 2. 



2 Yaman-ouchi, S., The life history of Polysiphonia. Bot. Gaz. 42:401-449- 

 1906. 



3 Lewis, I. F., Alternation of generations in certain Florideae. Bot. Gaz. 53 : 236- 

 242. 1912. 



Botanical Gazette, vol. 54] 





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