48 Morphology BOOK i 



the basis of his argument. It followed at once that he 

 was compelled to distinguish between two different kinds 

 of life-cycle. In the Thallophyta asexual forms follow in 

 succession for several generations ; then a sexual form 

 occurs, to be followed again by several asexual generations. 

 In the archegoniate plants, from the liverworts upwards, 

 the alternation of sexual and asexual forms is constant, and 

 the two phases are apparently fundamentally distinct. 

 Celakowsky applied the terms protophyt and antiphyt to the 

 two phases, names replaced later by gametophyte and sporo- 

 phyte in use to-day. He was clear as to the distinction : 

 ' The protophyt is never able to produce spores as well as 

 sexual cells, the antiphyt never sexual cells besides spores.' 

 Here is a clear pronouncement of a difference from the 

 thallophytic plants, where the separation of the sexual and 

 asexual reproductive cells is not so absolute. The alterna- 

 tion shown by these latter Celakowsky called homologous, 

 basing the term upon the similarity of organization of the 

 two alternating forms, in which the question of the nature 

 of the reproductive cells arising on them is determined in 

 great measure by variation of internal or possibly external 

 conditions. This aspect of the subject, as we shall see, 

 was very closely investigated later in the century by Klebs. 

 The similarity of organization is emphasized by the fact 

 that individuals bearing the sexual organs may, and often 

 do, produce asexual reproductive cells as well. 



The other kind of alternation, in which the asexual 

 phase invariably gives rise to the sexual, and vice versa, 

 indicating that the life-cycle is cast in a very definitely 

 settled mould, Celakowsky called antithetic, suggesting that 

 the one form is the natural complement of the other, and 

 that a single life-cycle necessarily embraces both. 



Celakowsky does not appear to have held the view that 

 the processes, already alluded to as discovered by Pring- 

 sheim in Oedogonium and Coleochaete, correspond to the 



