484 BOTANICAL GAZETTE [December 



life to a land life. Moreover, some of the thallophytes, such as 

 Coleochaete, Ascomycetes, and Florideae, he holds show the begin- 

 ning of an antithetic alternation. Strasburger (54), summarizing 

 cytological results, advanced the theoretical conception of the 

 periodic reduction of chromosomes in the life cycle in plants, thus 

 establishing the view that the x and 2% generations which complete 

 the life cycle of the plant are quite distinct from each other. This 

 view has proved the antithetic character of the two generations 

 from a cytological standpoint. 



Since that time, cytological investigations of algae which directly 

 touch the problem of the alternation of generations are those of 



Klebs (23), Williams (66), Wolfe (70), Lewis (27), Svedelius 



(60), and of the author (71, 73, 74, 76). 



Klebs conducted experimental cultures of several algae, such 

 as Vaucheria, Oedogonium, and others. By controlling factors such 

 as light, temperature, moisture, oxygen, and chemical composition 

 of nutritive media, he succeeded in producing any kind of reproduc- 

 tion, either sexual or asexual; in other words, he observed no regular 

 alternation of neutral and sexual generations. 



Williams discovered a reduction of chromosomes during the 

 tetraspore formation in Didyota, and this led him to conclude that 

 the tetrasporic plant of Didyota is a sporophytic generation derived 

 from the fertilized egg. 



Wolfe showed for Nemalion that the cells of the cystocarp 

 have double the number of chromosomes found in the sexual plant, 

 thus presenting the first cytological evidence that the cystocarp of 

 the red algae is sporophytic in character. He placed the period of 

 chromosome reduction at the time of carpospore formation, basing 

 his conclusion on a count of chromosomes in the mitosis just 

 previous to the formation of the carpospores. However, he did not 

 describe the phenomena characteristic of chromosome reduction, 

 namely, the period of synapsis followed by the two divisions which 

 distribute the chromosomes so as to give a numerical reduction. 



After the publication of Williams' and Wolfe's work, Stras- 

 burger expressed his agreement with Williams' conclusion con- 

 cerning the alternation of generations in the brown algae, but 

 remarked that the tetraspores of the red algae seemed to be different 



