No. 435-] ANTITHETIC VERSUS HOMOLOGOUS. l6l 



intimate that the apophysis of Splachnum is genetically related 

 to the leaves of the Pteridophytes ; but it is no more associated 

 with spore-production than they are. and shows the capacity of 

 the sporangium of the Bryophyte to produce special vegetative 

 organs in no way connected with spore-production. The segre- 

 gation of the spore-masses, already spoken of in connection with 

 Anthoceros, is at any rate a hint of the origin of the sporangia 

 of the Pteridophytes. As to the overwhelming tendency to 

 spore-production in Bryophytes, while this is undoubtedly true of 

 the simpler types, it may well be questioned whether it can prop- 

 erly be asserted of the most highly developed ones. It would 

 be an interesting problem, for instance, to compare the relative 

 output of spores in Polytrichum and Osmunda ciunamomca. 



While it is inconceivable that such an extremely specialized 

 structure as the sporophyte of the higher Mosses could have 

 given rise to the leafy sporophyte of the Pteridophytes, it is 

 quite conceivable that both types may have originated from a 

 common ancestral form, which may very well have been not very 

 different from Anthoceros. That the latter is "hopelessly 

 specialized " is very far from being the case. On the contrary, 

 the sporophyte of Anthoceros is a remarkably generalized 

 structure. I mean by this, that it has not a single character 

 which is peculiar and cannot be duplicated elsewhere. 



Pringsheim, the first advocate, I think, of the homologous 

 theory of alteration, based his conclusions upon the behavior of 

 various mosses in which the protonemal filaments may arise 

 directly from the sporophyte. Pringsheim believed that the 

 protonema was not essentially different from the vegetative 

 tissues of the sporophyte, from which they arose in such cases. 

 This reasoning is not entirely convincing. The protonema arises 

 normally from special sporophytic cells, the spores, and it is 

 difficult to see why, under abnormal conditions, it might not 

 arise from other sporophytic tissue. The same reasoning will 

 apply to apospory in the ferns where the gametophyte may 

 arise directly from the leaf-tissue. 



The strongest argument in favor of homologous alternation is 

 the occurrence of apogamy, or the origin of the sporophyte as a 

 vegetative bud from the gametophyte. So far as I am aware 



