igi2] YAMANOUCHI—CUTLERIA 483 



Perhaps the first clear statement of a regular alternation of 

 generations in thallophytes is by Sachs (42), who endeavored to 

 bring together the facts known in algae and fungi, and to compare 

 them with alternation in the Archegoniatae. Sachs states that 

 the life cycle of algae and fungi is similar to that of the Arche- 

 goniatae, one generation producing sexual organs, and the other 

 forming spores. Pringsheim (36) held quite a different view, 

 namely that the alternation of generations in the thallophytes 

 consists in the regular succession of a non-sexual or "neutral" 

 generation with a sexual generation, both generations being of 

 similar structure. 



Both these views, one by Sachs, who recognized two distinct 

 generations in thallophytes, and the other by Pringsheim, who 

 regarded the two alternating generations as similar structures, 

 have continued to find followers. . Vines (65) held the view that 

 most of the thallophytes have no alternation of generations, 

 since both sexual and asexual modes of propagation are directly 

 dependent upon the external conditions, and that an alternation 

 of generations in algae comparable to that in the bryophytes is 

 only found in Coleochaete and Char a. Celakovsky (5), although 

 opposing Pringsheim in his conception of alternation of genera- 

 tions in the Archegoniatae, which he designated as the "antithetic," 

 agreed with him in his conception of alternation in thallophytes, 

 in which the successive generations are alike and which conception 

 he designated as the "homologous." Pringsheim's conception of 

 the homologous alternation of generations in the Archegoniatae 

 has received its principal support in Lang's experimental cultures 

 (26) of the apogamous development of the sporophytes on pro- 

 thallia of several pteridophytes. Celakovsky's conception of 

 alternation of generations in the Archegoniatae was taken up fifteen 

 years later by Bower (4), who has supported this conception by 

 his theory of an interpolated sporophytic generation. Bower 

 holds that the antithetic alternation originated by the intercalation 

 of a non-sexual generation as a new development between two 

 gametophytic generations. This interpolation of a special sporo- 

 phyte probably took place, according to Bower, in the algae-like 

 ancestors of the Archegoniatae as they emerged from an aquatic 



