leaves," certain garden-flowers, etc. But none of them have persisted in
free nature, or evolved into permanent types.

On the other hand, wherever enduring types have arisen, we find traces of a
gradual origin by successive stages, even if, at first sight, their origin
may appear to have been sudden. This is the case with SEASONAL DIMORPHISM,
the first known cases of which exhibited marked differences between the two
generations, the winter and the summer brood. Take for instance the much
discussed and studied form Vanessa (Araschnia) levana-prorsa. Here the
differences between 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. 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