No. 435 ] ANTITHETIC VERSUS HOMOLOGOUS, 16s 



tophore, rather than the sporophyte," may be questioned. With 

 comparatively few exceptions, the sporophyte of the Bryophytes 

 is erect, while the shoots bearing the sexual organs, especially 

 among the liverworts, are very often prostrate. Moreover there 

 is in most of the latter class no development of distinct game- 

 tophoric shoots in the sense that such occur in the more special- 

 ized Marchantiacea: and mosses. The transition from strictly 

 thallose forms like Aneura or Pallavicinia to genuine leafy forms 

 like the typical Acrogynx is extremely gradual, the leafy shoots 

 of the latter forms being in no sense buds from a thallo.se game- 

 tophyte, but direct transformations of the whole body of the lat- 

 ter. We are, therefore, perfectly justified in homologizing the 

 leafy moss plant including of course the protonema, with a thal- 

 lose liverwort or with the prothallium of a fern. 



Dr. Coulter thinks that the spores would find more favorable 

 conditions upon a leafy shoot than upon a thallus, which is 

 doubtless true ; but why this leafy shoot should not develop 

 gradually from the sexually-produced sporophyte of the Bryoph- 

 ytes, as there is the strongest evidence that it has done, he does 

 not make clear. The development upon the leaves, of spores of 

 the same type as those of the lower Archegoniates, is entirely 

 comprehensible, if we assume that the leafy sporophyte of the 

 ferns is descended from a leafless bryophytic sporophyte; but it 

 is hard to understand if we assume that the spores of the ferns 

 have no genetic connection with the absolute!} similar ones of 

 the Bryophytes. 



According to Dr. Coulter's hypothesis, the leafy sporophyte 

 originates as a vegetative shoot from the gametophyte in a man- 

 ner analogous to the production of the gametophoric shoots in 

 the mosses, or the apogamous origin of the sporophyte in some 

 ferns. Upon the leaves, which originally were purely organs for 

 photosynthesis, were developed secondarily the sporangia. The 

 germination of the non-sexual spores and of the zygote are 

 assumed to have been entirely similar, giving rise first to a thal- 

 lus, from which secondarily the spore-bearing leafy shoot arose. 

 If such has been the course of development, it is strange that 

 all trace of the thallose portion has been lost in the sexually 

 produced sporophyte. One would expect to find some trace of 



