i9 1 2] . YAM ANOUCHI— CUTLER! A 485 



from those of the Dictyotaceae, and that the place of the chromo- 

 some reduction in the red algae should be sought elsewhere than 

 at the formation of tetraspores because some of the red algae 

 develop no tetraspores, but monospores instead. But immediately 

 after the appearance of this view of Strasburger, the author's 

 work on Polysiphonia was published. He found that the reduction 

 of chromosomes, instead of taking place at the formation of carpo- 

 spores as reported by Wolfe, occurred at the development of the 

 tetraspores. Thus in the life cycle of Polysiphonia, the sporophytic 

 generation is not only represented by cystocarpic branches, but 

 also extends to the tetrasporic plant that alternates antithetically 

 with the sexual plant. 



Lewis then worked out the cytology of Griffithsia, special atten- 

 tion being paid to the problem of the alternation of generations. 

 The place of the reduction of chromosomes is in tetraspore 

 formation as in Polysiphonia. He concludes that there is in 

 Griffithsia as in Polysiphonia an antithetic alternation of genera- 

 tions, the gametophytes being represented by the sexual plants and 

 the sporophytes by the sporogenous cells of the cystocarps. In 

 addition to this, there is a regular succession of tetrasporic indi- 

 viduals and sexual individuals; tetrasporic individuals resemble 

 the gametophytes in morphological differentiation and the sporo- 

 phytes in number of chromosomes. He regards the tetrasporic 

 and sexual plants as presenting homologous alternation. 



Svedelius studied the alternation of generations in Delesseria. 

 Although his work does not cover the whole life cycle of this type, 

 the cytological studies being made only in the development of 

 tetraspores and vegetative mitosis in both tetrasporic and female 

 plants, yet by comparing his work with that on Nemalion, Poly- 

 siphonia, and Griffithsia, he has come to the conclusion that there 

 is an alternation of generations in Delesseria as in Polysiphonia. 



The existence of an alternation of generations in the thallo- 

 phytes, though somewhat obscure in the green algae on account 

 of insufficient investigations, has been clearly proved by the cyto- 

 logical studies on Fucus and Dictyota among the brown algae, and 

 on Nemalion. Polysiphonia, Griffithsia, and Delesseria among the 

 red algae. Let us now turn to the situation in Cutlcria. 



