Chap, ii The Theory of Metamorphosis 69 



degree than had been formerly held. As we have seen, 

 the work of Darwin had given a special prominence to 

 this aspect of the subject, and its spirit dominated to a 

 greater or less degree almost all the research of the time. 

 As we trace the course of opinion on the theory of metamor- 

 phosis it is important to bear this in mind. Morphology 

 alone, morphology allied to phylogeny and ontogeny, were 

 alike seen to furnish insufficient answers to the problems 

 of development, and physiological considerations came 

 very prominently into the field. It is impossible to avoid 

 recognizing how these considerations modified the current 

 views on metamorphosis. 



Another line of investigation was not without its influence 

 in a similar direction. The alternation of generations, 

 whose development we have just discussed, drew attention 

 to and excited inquiry about the origin of the terrestrial 

 plant. As we have seen, the advocates of the antithetic 

 theory supposed the latter to have arisen from a structure 

 originating as little else than a mass of spores, and to 

 have begun its evolution from such a stage by sterilization 

 of sporogenous tissue, possibly passing through such 

 a stage as the sporogonium of a liverwort, or the strobilus 

 of a Lycopodium. In such a mode of origin there is no 

 room for the stem and leaf as fundamental or primitive 

 structures. The differentiation into members of these 

 categories must have been later in the course of evolution, 

 and again, adaptation to environment — a physiological 

 conception — must have been one at least of the causes 

 which led to the attainment of definite form. 



The difficulty which appeared in the writings of Goethe, 

 and later in those of Braun, in that neither puts forward 

 a definite conception of the ideal leaf, was reflected in 

 the writers who followed them, and was felt the more 

 seriously as the necessity for making a clear distinction 

 between stem and leaf was realized. Many attempts were 



