most 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. Korschinksky attributes
to them weaknesses of organisation in general; "they bloom late, ripen
few of their seeds, and show great sensitiveness 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 transformation
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 weaknesses of this theory
("Vortrage uber Descendenztheorie", Jena, 1904, II. 269. English
Translation London, 1904, II. page 317.), and I am the less inclined
to return to it here that it now appears (See Poulton, "Essays on
Evolution", Oxford, 1908, pages xix-xxii.) 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
"m