etation, we shall see the full significance of the almost
total absence of thorny and spiny plants in the chief oceanic islands;
and so far from "excluding the hypothesis of mammalian selection
altogether," we shall find in this hypothesis the only satisfactory
explanation of the facts.

From the brief consideration of Professor Geddes's theory now given, we
conclude that, although the antagonism between vegetative and
reproductive growth is a real agency, and must be taken account of in
our endeavour to explain many of the fundamental facts in the structure
and form of plants, yet it is so overpowered and directed at every step
by the natural selection of favourable variations, that the results of
its exclusive and unmodified action are nowhere to be found in nature.
It may be allowed to rank as one of those "laws of growth," of which so
many have now been indicated, and which were always recognised by Darwin
as underlying all variation; but unless we bear in mind that its action
must always be subordinated to natural selection, and that it is
continually checked, or diverted, or even reversed by the necessity of
adaptation to the environment, we shall be liable to fall into such
glaring errors as the imputing to "ebbing vitality" alone such a
widespread phenomenon as the occurrence of spines and thorns, while
ignoring altogether the influence of the organic environment in their
production.[211]

The sketch now given of the chief attempts that have been made to prove
that either the direct action of the environment or certain fundamental
laws of variation are independent causes of modification of species,
shows us that their authors have, in every case, failed to establish
their contention. Any direct action of the environment, or any
characters acquired by use or disuse, can have no effect whatever upon
the race unless they are inherited; and that they are inherited in any
case, except when they directly affect the reproductive cells, has not
been proved. On the other hand, as we shall presently show, there is
much reason for believing that such acquired characters are in their
nature non-heritable.

_Variation and Selection Overpower the Effects of Use and Disuse._

But there is another objection to this theory arising from the very
nature of the effects produced. In each generation the effects of use or
disuse, or of effort, will certainly be very small, while of this small
effect it is not maintained that the