THE AMERICAN NATURALIST [Vol. XLIV 



The members of each pair are separated by the first 

 mitosis which thus distributes the thirty-two chromo- 

 somes in two sets. The second mitosis (homotypic) pre- 

 sents sixteen simple chromosomes in the form of bent 

 rods, similar to those found in the gametophytes. The 

 cytological evidence justifies the conclusion that the 

 tetraspores give rise to the sexual plants and that the 

 fertilized egg must develop the asexual plant, and thus 

 is established an alternation of generations. 10 



The peculiarities of the life history of Fucus in rela- 

 tion to the life histories of plants in general are most 

 striking. It became evident from the studies of Stras- 

 burger in 1897 and of Farmer and Williams in 1896-98 

 that the mitoses within the oogonium presented only half 

 the number of chromosomes which were present in the 

 vegetative cells of the Fucus plant. This placed the 

 period of chromosome reduction just previous to the dif- 

 ferentiation of the gametes, a condition that is not known 

 in any other group of the thallophytes. To bring such a 

 life history into relation with the prevailing conditions 

 in the lower plants becomes a most interesting problem 

 of plant morphology and phylogeny. 



We have recently had from Yamanouchi 11 a much more 

 detailed account of the reduction processes in Fucus than 

 the descriptions of the earlier writers. The nucleus 

 within the young oogonium passes through a remarkably 

 clearly defined stage of synapsis during which chromatic 

 threads, derived from a reticulum, become arranged in 

 loops that are gathered together closely attached at one 



