NOTES AND LITERATURE 



LIFE HISTORIES IN THE RED ALQJE. 



The past decade has given us a number of excellent life his- 

 tory studies in the Rhodophycem which have been of material 

 assistance in clarifying a very difficult field in plant morphology. 

 The more important of these contributions will form the subject 

 of this review. 



Yamanouchi 1 in 1906 published an account of the life history 

 of Polysiphonia violacea based on cytological investigations of all 

 of its significant phases. He arrived at the following chief con- 

 clusions: (1) Carpospores have 40 chromosomes and tetraspores 

 20, i. e., half of this number. (2) The sexual plants in their 

 vegetative mitoses showed 20 chromosomes and therefore were 

 believed to arise from tetraspores. (3) The asexual or tetrasporic 

 plants showed 40 chromosomes throughout their vegetative his- 

 tory and consequently could be assumed to come from carpo- 

 spores. (4) The production on the asexual plants of tetraspores 

 is the result of a reduction division since the first mitosis in the 

 tetrasporangium is clearly heterotypic as shown by the character- 

 istie pairing of the 40 chromosomes and the separation of the 

 members of each pair; thus each tetraspore comes to have 20 

 chromosomes and is prepared to develop a sexual plant. (5) It 

 was therefore clear that the formation of tetraspores determines 

 the end of a sporophytic generation in the manner characteristic 

 of plants. (6) The gamete nuclei of the sperms and carpogonia 

 take the 20 chromosomes of the sexual plants and fertilization 

 gives the zygote nucleus with 40 chromosomes. (7) Descendants 

 from the zygote nucleus enter the carpospores which conse- 

 quently have 40 chromosomes and on germination would give 

 tetrasporic plants; certain complicated cell fusions during the 

 development of the cystocarp are purely cytoplasmic in char- 

 acter and evidently nutritional in function. (8) "There is thus 

 an alternation of a sexual plant (gametophyte) with a tetrasporic 

 plant (sporophyte) in the life history of Polysiphonia, the cysto- 

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

 Yamanouchi's contribution on Polysiphonia has in great meas- 

 i Yamanouchi, S., "The Life History of Polysiphonia violacea." Bot. Gaz., 

 XLII, 401-449, 1906. 



