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!, and I am the less inclined to return to it here 
that it now appears? 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? was right in regard- 
ing transformations as taking place by minute steps, which, if useful, 
ae Vortrige iber Descendenztheorie, Jena, 1904, 11. 269, Eng. Transl. London, 1904, 11. 
p. 317. 
® See Poulton, Essays on Evolution, Oxford, 1908, pp. xix—xxii. 
* Origin of Species (6th edit.), pp. 176 et seq. 
