Cockayne. — Ecological Studies in Evolution. 37 



characteristic that, however much intensified, could bring about no specific 

 differences unless correlated with structural change. In point of fact, 

 the deciding factor in the struggle amongst a close-growing mass of 

 these tree seedlings is probably age. Could all commence on exactly the 

 same footing, then the determining factor would be the situation with 

 regard to the food-supply and the illumination, and no slight beneficial 

 modification would count in comparison. 



As for the adult forest-trees, each has, as a rule, its own rooting-place, 

 and its death depends chiefly upon its . age, partly upon some disease 

 or other, and but little upon the superior adaptations of its neigh- 

 bour. Its growth-form, certainly, does have something to do with its 

 longevity, as where spreading branches favour the presence of abundant 

 epiphytes, whose weight may lead to damage and permit the attack of 

 fungi. 



A mixed rain forest, apart from modifications due to the nature of the 

 topography, might be expected to offer constant conditions extending 

 over a considerable period. But this is not so ; topographically similar 

 parts of a forest may show dissimilar undergrowth, the result of conditions 

 which, similar at first, become dissimilar as the vegetation develops. Thus 

 in the Waipoua Kauri Forest, of which I made a special study, a state 

 of change ruled. In one part there was little undergrowth, and in another 

 part such in abundance. This latter, in time, will, through survival of the 

 fittest, change into forest with little undergrowth. These are two climaxes, 

 and are expressions of the light factor, the dense undergrowth denoting 

 the maximum and the final open forest with the close roof the minimum 

 of illumination. Between these two climaxes there are many transitions. 

 Bring in more light still and so increase the xerophily, the hygrophytes will 

 go to the wall, until, with excess of light, a transition forest and finally 

 a Leptospermum heath will be established (Cockayne, 1908, p. 30). From 

 the above it follows that, even were natural selection at work amongst the 

 young plants of any species, owing to the varying change of conditions 

 brought about by these plants themselves there would be an insufficient 

 length of time for any more suitable variety to arise, or, if such selection 

 were very rapid, different types would be selected within a quite limited 

 area. The believer in the efficacy of epharmonic variation would say that 

 forest-trees have arisen from shrubs, or vice versa, owing to the stimulus 

 of edaphic, climatic, and other factors, and that selection operated by elimin- 

 ating those individuals which did not respond epharmonically at various 

 stages of the plants' development. And the special evidence put forth 

 would be that many species possess an unfixed epharmonic tree form and 

 shrub form, while it is known that stature and other features can be modified 

 through changes in nutrition. This, after all, is only Darwinian selection 

 plus an assigned cause for rapid and sometimes favourable modification* ; 

 but it is far from being neo-Darwinian selection. 



VIII. Distribution of Speciks. 



1. Distribution in General. 



The distribution of species is primarily a matter of epharmony. Such, 

 however, must in certain cases be referred to a state of affairs no longer 



* I do not mean to infer that all modification is favourable. 



