No. 525] SEXUAL REPRODUCTION IN ALGJE 



527 



The investigations of Yamanouchi 14 on Polysiphonia 

 established the important fact that the carpospore of this 

 form retained the diploid number of chromosomes 

 (forty) present throughout the sporophytic tissue of the 

 cystocarp, and gave rise to a sporeling beat ing this num- 



were found to be diploid in character and the presence of 

 the period of chromosome reduction was established in 

 the tetraspore mother-cell. The nucleus of the tetra- 

 spore mother-cell passes through a clearly defined stage 

 of synapsis, following which the forty sporophytic chro- 

 mosomes are found associated in twenty pairs (bivalent 

 chromosomes). The first mitosis distributes the members 

 of these pairs and is therefore a reduction division. The 

 tetraspore has then the haploid number of chromosomes 

 (twenty) and on germination develops a sporeling with 

 this reduced number, which was found to be characteris- 

 tic of the sexual plants. It is reasonable to conclude that 

 in the life history of Polysiphonia the sexual plants alter- 

 nate with the tetrasporic, each phase arising from the 

 spores produced upon the other. Yamanouchi expressed 

 the belief that "the sexual plants and tetrasporic plants 

 present two distinct phases of an antithetic alternation 

 of generations, with the cystocarp a part of the sporo- 

 phytic phase". 



The many interesting points in the history of the de- 

 velopment of the sexual organs and the cystocarps are 

 too detailed to be presented in this brief review. Yama- 

 nouchi, however, supports Wolfe's conclusion that the 

 trichogvne in early stages of development contains a 

 nucleus, and that the sperm is the homologue of an anthe- 

 ridium, although in Poli/siphonia this cell is uninucleate. 

 Sin™ Pritw-isms of I\ urssanow 1 " on the work of Wolfe 



