THE SPERMATOPHYTA : GENERAL INTRODUCTION 645 



a herbaceous species passes through many more generations in a given 

 time than does a tree species. Every flowering period imphes sexual repro- 

 duction, with its concomitant possibihties of variation, and thus there has 

 been a marked acceleration of the tempo of evolution in these short-lived 

 types. 



The foregoing remarks all tend to emphasize the importance of the relation 

 between the plant and its environment, that is to say, the kind of consideration 

 which is called Ecological. Ecology, in fact, almost dominates the botanical 

 treatment of the Angiosperms, to the subordination of the purely morpho- 

 logical outlook which usually prevails in the treatment of lower groups. 

 The principal reason for this difl"erence seems to be that the vast multiplicity 

 of forms among the Angiosperms makes it impossible for any individual worker 

 to study thoroughly the morphology of more than a very small proportion 

 of them. The time has not yet come when a comprehensive morphological 

 treatment may be possible, except perhaps in relation to some of their sexual 

 structures, in which there is some degree of uniformity. The vegetative 

 morphology can only be treated in the barest outlines and with reference to 

 one or two fundamental attributes. 



Morphology of the Shoot in the Spermatophyta 



The old-fashioned morphologist studied form purely as an aid to classi- 

 fication, and he therefore classified the types of form which he observed as 

 fixed and static things, assigning to each type of form a name and a definition. 

 Such types represented a series of Platonic ideals or concepts to which the 

 visible world was assumed to conform. The kinetic views of modern 

 evolutionary biology have swept all this away into the limbo of forgotten 

 artificialities. We now regard all forms as part of a universal evolutionary 

 flux, and the end we pursue is, not the precise discrimination of forms from 

 one another, but the opposite, namely, an understanding of their relationships 

 to each other and of their transformations during the march of time. 



When we apply such an idea to the study of spermatophytic structure, we 

 can see that it is possible to get an idea of the evolutionary morphology of 

 some at least of their structural elements, in relation to the structure of lower 

 groups. 



The Spermatophyta are " cormophytes," that is to say that they, like the 

 Pteridophyta, have three sorts of vegetative organs, stems, leaves and roots, 

 but to treat these as fixed categories would be a reversion to the older 

 morphology which we have condemned. If we go back into the past and 

 endeavour to judge by the fossil evidence and by comparisons with lower 

 groups of living plants, we may expect to find these categories merging 

 together and blending into some common unity, as we go lower and lower 

 in the scale of organization. That is to say that we should not regard them 

 as fundamentally distinct but as having had a common evolutionary origin. 



Although the Spermatophytes share this cormophytic organization with 

 the Pteridophytes, they difl^er from them markedly in one aspect of internal 



