326 SCIENCE PROGRESS. 



alternation. The question of the mode of origin of the 

 complicated and ultimately independent sporophyte of the 

 latter group is not entered upon by Pringsheim. 



The antithetic theory was restated 1 in the light of 

 Pringsheim's views in 1877. Celakovsky recognises clearly 

 the two main points contended for by that author, but 

 while he admits that the fruit of Flofidecs, Ascomycetes and 

 Hymenomycetes does not represent the second generation 

 (antiphyt), he maintains the view that the antithetic alter- 

 nation in Mosses and Vascular Cryptogams is essentially 

 distinct from the homologous alternation of Thallophytes. 

 Certain additions to the antithetic theory must be men- 

 tioned, since they are the basis on which later work has in 

 great part proceeded. The fruit body of Coleochcete is not 

 recognised as a generation since all its cells produce swarm 

 spores, but it is pointed out that from the Coleochcete fruit 

 to the Riccia sporogonium is but a step. " This step is 

 made in this way, an outermost layer of the spore-producing 

 parenchyma transforms itself into a covering layer (wall of 

 the sporogonium) and thus remains sterile instead of its 

 cells changing to spores." The extension of this modifica- 

 tion of spore-producing cells would lead to the kind of 

 sporogonium found in the higher Bryophyta. Thus the 

 Moss fruit is not homologous with the neutral generation of 

 a Thallophyte, but is " a third newly arrived generation 

 interpolated between the sexual and the first neutral genera- 

 tion ". To illustrate this the series of forms Vaucheria, 

 CEdogonium, and Cystopus, Coleochcete, and Riccia are 

 used. Celakovsky does not admit the importance which 

 Pringsheim attached to the phenomena of Apospory and 

 Apogamy, as evidence of the homology of the sexual and 

 spore-bearing generations. The former is to be explained 

 by the origin of all the vegetative cells of the sporophyte 

 from primitively reproductive cells, while Apogamy proves 

 nothing further than that the second generation can arise 

 from an indifferent cell of the prothallus, instead of from a 

 special sexual cell by a sexual process. He points out that 

 in these cases the alternation is not lost, the archegonial cell 



1 Celakovsky (3). 



