52 Morphology BOOK i 



attracted a good deal of attention, and though at first only 

 these two isolated cases were known, the discovery led to 

 a re-examination of the question of the relation of the 

 sexual to the asexual forms of archegoniate plants. 



The view which has since this date always been associated 

 with the name of Pringsheim was advanced by him in 

 1877, on the basis of his former investigations, supple- 

 mented by these new discoveries. He claimed that there is 

 a fundamental agreement between the irregular but homo- 

 logous alternation in the Thallophytes and the regular 

 sequence in the Mosses and Vascular Cryptogams, recog- 

 nizing only a difference of degree between them. The two 

 phases in the latter groups are according to him homologous 

 with one another, and the same homology exists between the 

 sporangia of the one and the antheridia and archegonia of 

 the other. Indeed he went so far as to claim that the 

 seta of a moss capsule is homologous with the axis of the 

 plant which bears the leaves. He put his position very 

 clearly as to the condition in the Mosses, claiming that 

 the alternation is due to the reduction of the series of 

 asexual forms of the Thallophytes to a single one, which 

 remains in inseparable connexion with the sexual one which 

 originates it. He said further, emphatically, that the 

 moss sporogonium stands in about the same relation to 

 the moss plant as the sporangium-bearing individuals of 

 Saprolegnia stand in to those which bear oogonia, or as 

 among the Florideae the specimens with tetraspores are 

 related to those with sporocarps. 



Dealing with the Thallophytes, Pringsheim called atten- 

 tion to the great diversities which exist in the relations 

 of the sexual and the asexual individuals to one another. 

 Some bear only one form of reproductive cell ; others may 

 bear both. Most frequently numbers of individuals bearing 

 asexual cells are developed in a long sequence, and a sexual 

 plant only occurs at intervals. The sexual individual never 



