58 Morphology book i 



Phylogenetic considerations confirm the conclusion to which 

 these facts lead, showing that the gametophyte is the older 

 generation, corresponding closely with the gametophyte of 

 the Liverworts if not so evidently with that of the green 

 Algae. The sporophyte is younger and does not correspond 

 with any structure in the latter group. Viewing a large 

 number of forms, a comparison of them shows the progress 

 of the sporophyte from small beginnings in the lower 

 Bryophyta to large size and great complexity of form and 

 structure in the Vascular Cryptogams and Gymnosperms. 



The whole advance is accompanied by a corresponding 

 reduction of the gametophyte. Bower concluded from 

 these facts that the establishment of the alternation is the 

 result of the adaptation which followed the change from 

 conditions originally aquatic to a sub-aerial habitat. He 

 went so far as to say that the alternation might be dis- 

 tinguished physiologically as an amphibious alternation, 

 which finds its morphological expression in the differences 

 of external form and internal structure observable between 

 the more ancient gametophyte and the more recent sporo- 

 phyte. 



It is quite in harmony with this position that Bower 

 refused to see as definitely as Sachs did the origin of the 

 sporophyte among the Algae. Neither in the case of 

 Oedogonium nor in that of the Florideae did he admit any 

 true homology. He pointed out with some emphasis that 

 the circumstances of formation are different in the two 

 cases, while the bodies produced from the spores or carpo- 

 spores of Oedogonium are motile and not fixed plant forms. 

 Bower accordingly held there was in these Algae only a 

 parallel development, not leading on to the establishment 

 of the sporophyte of the archegoniate plants. 



Bower's views so far were supported by Atkinson some 

 years later, and the additional argument was adduced by 

 the latter writer, that the disturbance of the new terrestrial 



