Cockayne. — Ecological Studies in E volution . 13 



Red clover (Trifolium pratense L.) and cowgrass (the var. perenne) vary 

 to an astonishing extent in a small patch, chiefly self-sown, in my garden. 

 Many of the forms are most distinct, and the new characters are diverse, 

 affecting colour of flowers, stems, and foliage, form of inflorescence, degree 

 and kind of hairiness, general habit, &c. Here pure culture-methods and 

 Mendelian procedure would be needed to come to any reliable conclusions 

 as to variants such as these. 



Holcus lanatus L. and Dactylis glomerata L., I am informed, vary at 

 times beyond their ordinary fluctuating capacity. 



Capsella Bursa-pastoris Medic, a very variable species in its natural 

 habitat, and which has already given rise to certain mutants, varies to an 

 astonishing degree in New Zealand, especially in highly manured ground. 

 A careful study of such variation is certainly demanded. 



Y. Epharmony. 

 1. General. 



It is when we come to epharmonic adaptations that ecology presents 

 its most important contribution to the evolution question. 



In attempting to explain the origin of epharmonic adaptations it is 

 evident that, as in the case of all explanations of evolutionary phenomena, 

 no absolute proof can be given without experiment, and, where such is 

 wanting, it seems reasonable that the most probable explanation should 

 be accepted for the time being, notwithstanding that other though less 

 probable explanations would fit the case. Generally in polemical dis- 

 cussions on matters of evolution natural selection is assumed to be a vera 

 causa which needs no demonstration, and if any other reason is put for- 

 ward, however likely it may appear, it is considered of no moment, unless 

 it can be proved not merely to the hilt, but to the objector's satisfaction. 



Now, I am of opinion that in the hereditary epharmonic variations 

 cited below there is a much greater likelihood of their having been brought 

 about by the direct action of the various ecological factors than by the 

 continuous accumulative selection of fluctuating varieties, and in making 

 this statement I am merely echoing the opinion regarding analogous phe- 

 nomena of Romanes (1895, pp. 122-32), Warming (1909, pp. 370-73). 

 MacDougal (1911, p. 57), Henslow (1895, 1908), Costantin (1898), (Scott- 

 Elliott, 1910), and many other writers on evolution. 



With the much-disputed Lamarckian factors use and disuse, which are 

 so frequently the only parts of the doctrine dealt with by the zoological 

 opponents of modified Lamarckism, I have nothing to do. How far evolu- 

 tionary methods correspond in the plant and animal kingdoms no one can 

 say, but it does not seem unreasonable to imagine that they may have been 

 in many respects different.* At any rate, this paper is concerned only with 

 the botanical side of evolution. 



2. Fixity of Species — Plasticity. 



Nothing has been brought out more clearly by ecological studies in 

 New Zealand than the extreme " plasticity " of many species and struc- 

 tures, and their rapid response to a change of environment. This is so 



* Leavitt (1907, p. 237) writes, " In no case is it safe to reason deductively from 

 one kingdom to the other. In the factors affecting their evolutioTi, plants and animals 

 differ vastly. 



