CHAP, i The Nature of Alternation of Generations 53 



gives rise directly to any but an asexual form. All these 

 forms, therefore, are clearly homologous with one another. 

 In the cases of Oedogonium and Coleochaete, to which the 

 origin of the intercalated generation was traced by the 

 advocates of the antithetic theory, Pringsheim saw in the 

 production of the zoospores of the former and the fruit- 

 body of the latter only the first asexual generation, the 

 difference in its development being due merely to reduction. 

 In Sphaeroplea the alternation is simpler, taking the form 

 of an alternation between a single sexual and a single 

 asexual generation. 



Pringsheim disputed also the propriety of regarding the 

 sporocarp of the Florideae as corresponding to the sporo- 

 phyte of either Coleochaete or the Moss or Fern, as had 

 been suggested by Sachs. He claimed that it was palpably 

 a part of the thallus on which it arises and has none of the 

 marks of a distinct organization. Yet we may notice that 

 it presents very distinctly one of the features claimed by 

 the advocates of the antithetic theory as a step in the 

 development of an intercalated sporophyte, that of securing 

 by a single act of impregnation the development of a 

 number of reproductive cells. 



It thus appears that Sachs and Pringsheim were exponents 

 of fundamentally different views. Sachs argued from the 

 very different phases or generations in the Mosses and 

 Ferns, traced these phases up to the Phanerogams, and then 

 claimed to show their existence among the lowlier forms, 

 explaining away what appeared in the latter group to be 

 conflicting with his views. Thus he arrived at a conception 

 of a uniform process throughout the vegetable kingdom. 

 Pringsheim, on the other hand, though he also claimed the 

 uniformity of the ultimate result, saw it brought about in 

 quite a different way. Recognizing in the lowly Thallo- 

 phytes homologous forms bearing sexual and asexual organs, 

 he carried the idea of such homology upwards and held it 



