24 The Selection Theory 



the two forms are so great and so apparently disconnected, that one 

 might almost believe it to be a sudden mutation, were it not that old 

 transition-stages can be called forth by particular temperatures, and 

 we know other butterflies, as for instance our Garden Whites, in 

 which the differences between the two generations are not nearly so 

 marked; indeed, they are so little apparent that they are scarcely 

 likely to be noticed except by experts. Thus here again there are 

 small initial steps, some of which, indeed, must be regarded as 

 adaptations, such as the green-sprinkled or lightly tinted under- 

 surface which gives them a deceptive resemblance to parsley or to 

 Cardamine leaves. 



Even if saltatory variations do occur, we cannot assume that these 

 have ever led to forms which are capable of survival under the 

 conditions of wild life. Experience has shown that in plants which 

 have suddenly varied the power of persistence is diminished. Kor- 

 schinksky attributes to them weaknesses of organisation in general ; 

 " they bloom late, ripen few of their seeds, and show great sensitive- 

 ness to cold." These are not the characters which make for success 

 in the struggle for existence. 



We must briefly refer here to the views much discussed in the 

 last decade of H. de Vries, who believes that the roots of trans- 

 formation must be sought for in saltatory variations arising from 

 internal causes, and distinguishes such mutations, as he has called 

 them, from ordinary individual variations, in that they breed true, 

 that is, with strict inbreeding they are handed on pure to the next 

 generation. I have elsewhere endeavoured to point out the weak- 

 nesses of this theory 1 , and I am the less inclined to return to it here 

 that it now appears 2 that the far-reaching conclusions drawn by 

 de Vries from his observations on the Evening Primrose, Oenothera 

 lamarckiana, rest upon a very insecure foundation. The plant from 

 which de Vries saw numerous "species" his "mutations" arise 

 was not, as he assumed, a wild species that had been introduced to 

 Europe from America, but was probably a hybrid form which was 

 first discovered in the Jardin des Plantes in Paris, and which does 

 not appear to exist anywhere in America as a wild species. 



This gives a severe shock to the " Mutation theory," for the other 

 actually wild species with which de Vries experimented showed no 

 " mutations " but yielded only negative results. 



Thus we come to the conclusion that Darwin 3 was right in regard- 

 ing transformations as taking place by minute steps, which, if useful, 



1 Vortrage ilber Descendenztheorie, Jena, 1904, n. 269. Eng. Transl. London, 1904, n. 

 p. 317. 



2 See Poulton, Essays on Evolution, Oxford, 1908, pp. xix xxii. 



3 Origin of Species (6th edit.), pp. 176 et seq. 



