56 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



As the above came to Darwin, as he says, " long after he came to 

 Down " (1842), and the " Variation " &c. was issued in 1868 and the 

 " Origin" in 1859, perhaps we may suggest about 1864 as the year. 

 For this view of adaptations is well developed in the " Variation " &c, 

 as stated. 



In 1876 Darwin wrote to Professor M. Wagner as follows, clearly 

 showing the utmost importance with which he then regarded " definite 

 variations " : 



" In my opinion the greatest error which I have committed 

 has been not allowing sufficient weight to the direct action of the 

 environment, i.e. food, climate, &c., independently of Natural 

 Selection. 



" When I wrote the ' Origin,' and for some years afterwards [four 

 or five ?], I could find little good evidence of the direct action of the 

 environment. Now there is a large body of evidence." * 



Yet it must have been, what we may perhaps call, a semi-conscious 

 sense of this truth, when the idea of "Descent with Modification" 

 crossed his mind when in South America. When he discovered the 

 remains of gigantic members of the Edentata, now represented by the 

 small Sloths, he seems to have thought the latter might have been 

 descended from the former. 



Self- adaptation, the Conclusion from Ecology. — The modern 

 method of " studying " plants or " Ecology," i.e. not only plants but 

 their "homes" as well, has immensely strengthened the view that 

 the origin of species is due to self-adaptation to changed conditions of 

 life. There is nothing new in the study itself, only the name. In 

 1820 M. P. A. de Candolle was the first real ecologist ; for he wrote 

 an article on Botanical Geography in the " Dictionnaire des Sciences 

 Naturelles," in which he traces the influences of all the various factors 

 of the external conditions of plant life, just as Dr. Schimper and 

 Professor Warming have done to-day ; only these and other modern 

 ecologists now carry us farther, for — believing, as we all do now, in 

 Evolution — one cannot look for Causes without perceiving that 

 xerophytic, hygrophytic, hydrophytic &c. conditions themselves supply 

 the " direct action," as Darwin called it, to which the plants respond, 

 and so are evolved all the characteristic structures so familiar to us in 

 each of the plant-associations respectively. Moreover, experiments 

 with plants are so easy to make, that the conclusions arrived at from 

 inductive observations in Nature can often be verified by them. 

 Nature, too, often makes experiments and always with the same 

 results. 



Dr. Schimper thus writes : " Experience shows that [morpho- 

 logical] differentiation is profoundly and rapidly modified by changes 

 in the environment, every one of which immediately involves a change 

 in the organization of the plants. ... It is by the adaptations that 

 the causes of the differences in the fades of the vegetation at different 

 points on the earth are rendered more comprehensive ; so that their 

 * Life and Letters, vol. iii. p. 158 (1876). 



