372 SCIENCE PROGRESS. 



produced ; while permanence by perennation was a general 

 consequence of it. 



The importance of this novelty may seem a ready ex- 

 planation of the absence of the earlier steps of its progress ; 

 just as, in the perfecting of bicycles or electric lighting, the 

 earlier improvements soon fall out of the competition, and 

 disappear before their more advanced successors, so with 

 most of the primitive leafy Pteridophytes. However little 

 we may be able to pronounce upon the history of genesis 

 of the primitive leaf (or its modes of origin, for they may 

 not all have conformed to the same original type), there is 

 one point which is prominent. There is a certain correla- 

 tion between spore-production and vegetative development ; 

 where sporangia are borne, the vegetative development is 

 restricted, but the latter is greater in their absence. Some 

 will say, "This is a mere phenomenon of nutrition," and 

 think that the matter may there be dismissed. But the 

 development of all parts of plants is in a sense "a pheno- 

 menon of nutrition," and none the less calls for morphologi- 

 cal study. The question will arise with regard to these 

 correlative parts, is either the more primitive foliar form, 

 and if so, which? It has commonly been assumed — in 

 accordance with that uncertain guide, the theory of recapitu- 

 lation—that the prior existent in the individual (foliage 

 leaf) was the prior existent in the race, and that the 

 sporophyll is therefore an altered foliage leaf. Others may, 

 however, be disposed to hold a converse view, and assert 

 that the foliage leaf is a sterilised sporophyll. There 

 certainly would appear to be a strong element of a priGri 

 probability in the latter view, in the fact that spore-production 

 was the first object of existence of the sporophyte ; the 

 production of spores is the end to which it always tends 

 (leaving on one side rare cases of apospory) ; and the spore- 

 stage is a constantly recurring event in the life-cycle. 

 This we have every reason to believe has been the case 

 throughout the course of evolution. As regards the history 

 of the sporophyte, spore-production appears to have preceded 

 any vegetative development of the sporophyte. 



But in dealing with such a large and complex question, 



