urse many
more experiments would have to be tried; but in former years I tried on
the whole leaf, instead of on separate glands, a number of innocuous
substances, such as sugar, gum, starch, etc., and they produced no
effect. Your opinion will aid me in deciding some future year in going
on with this subject. I should not have thought it worth attempting, but
I had nothing on earth to do.

My dear Hooker, yours very sincerely,

CH. DARWIN.

P.S.--We return home on Monday 28th. Thank Heaven!

THE STRUGGLE FOR EXISTENCE

From the 'Origin of Species'

Before entering on the subject of this chapter, I must make a few
preliminary remarks, to show how the struggle for existence bears on
Natural Selection. It has been seen in the last chapter that amongst
organic beings in a state of nature there is some individual
variability; indeed, I am not aware that this has ever been disputed. It
is immaterial for us whether a multitude of doubtful forms be called
species, or sub-species, or varieties; what rank, for instance, the two
or three hundred doubtful forms of British plants are entitled to hold,
if the existence of any well-marked varieties be admitted. But the mere
existence of individual variability and of some few well-marked
varieties, though necessary as the foundation for the work, helps us but
little in understanding how species arise in nature. How have all those
exquisite adaptations of one part of the organization to another part,
and to the conditions of life, and of one organic being to another
being, been perfected? We see these beautiful co-adaptations most
plainly in the woodpecker and the mistletoe; and only a little less
plainly in the humblest parasite which clings to the hairs of a
quadruped or feathers of a bird; in the structure of the beetle which
dives through the water; in the plumed seed which is wafted by the
gentlest breeze: in short, we see beautiful adaptations everywhere and
in every part of the organic world.

Again, it may be asked, how is it that varieties, which I have called
incipient species, become ultimately converted into good and distinct
species, which in most cases obviously differ from each other far more
than do the varieties of the same species? How do those groups of
species, which constitute what are called distinct genera, and which
differ from each other more than do the species of the same genus,
arise? All these results, as we shall more fully see in