CHAP, ii The Theory of Metamorphosis 77 



logical nature of the cause of their origin is emphasized 

 by Goebel's discovery that leaf-formation in the Liverworts 

 has arisen in quite a number of series independently of 

 one another (Organographie, p. 261). 



The same cause was suggested by Bower for the sporo- 

 phyte phase of the plant. Originating as a zygote, giving 

 rise to a large number of spores, a sporangium in fact, the 

 needs of the structure under open-air conditions were 

 primarily those of nutrition. The small supply of food 

 that could be derived from the gametophyte caused an 

 independent development of vegetative organs which was 

 initiated by a sterilization of part of the sporogenous 

 tissue. Whether the evolutionary process went on in 

 one or in several phyla is not of much importance to the 

 question before us. In any case the sterilization of the 

 sporogenous tissue led to the acquirement of vegetative 

 features by the sterilized cell-aggregates. The output of 

 special protuberances by these postulates nothing im- 

 probable, though no evidence is forthcoming on this point. 

 Granted that outgrowths did appear, the gradual differen- 

 tiation of both form and structure under functional 

 necessity must have followed. 



According to this theory, form has been determined by 

 physiological rather than morphological conditions, and 

 has been almost entirely traceable to the action of the 

 environment upon originally undifferentiated organisms. 

 It postulates, however, an inherent capacity for increasing 

 complexity of structure, together with a potentiality of 

 development in response to such stimulation as a widely 

 varying environment may present in different cases. The 

 individual qualitative differences in such capacity must 

 have been considerable, as the same external surroundings 

 have not produced uniformity of form or substance in 

 detail. Such differences, further, must have been deep- 

 seated in the organism, as the forms of the plants of to-day 



