No. 435] ANTITHETIC VERSUS HOMOLOGC 



According to the antithetic theory of alteration, 

 originated from forms very similar to the simple - 

 worts, the leafy sporophyte being an elahorati< 

 sexual sporophyte. The homologous theory 

 Bryophytes and Pteridophytes have nothing to 

 other, the latter arising quite independently from ; 

 The latter hypothesis was first suggested by tlv 

 tonema of the mosses, and the somewhat similr 

 certain ferns, especially Trichomanes. 



Opposed to this assumption is the fact that 

 prothallia of such ferns as Trichomanes, or Schir,- 

 obviously secondary developments, in the former 

 associated with excessive moisture. The prothalli; 

 grown in water, or kept excessively wet, and poorl 

 to assume a filamentous form. Among both Hy 

 and Schi/a-aeea\ the great majority of forms s' 

 the normal flattened prothallium of the ordinar; 

 filamentous protonema of the true mosses is als- 

 trust the evidence of comparative morphology 

 development from the liverwort-like thallose protc 

 like Sphagnum. The true mosses and Hymen, 

 probably very far from being primitive types. 



From a comparison of the fossil and living fe 

 that the so-called eusporangiate types are much 

 leptosporangiate forms which are now predominar 

 tiaceae, of which only a small number of tropical : 

 are especially well represented in the Palaeozoi* 

 on the assumption that the gametophyte of the fer 



