tion: "I can show the meaning of some of the apparently meaningless
ridges (and) horns; who will now venture to say that this or that
structure is useless?" It is the fashion now to minimise the value of
this class of work, and we even find it said by a modern writer that to
inquire into the ends subserved by organs is not a scientific problem.
Those who take this view surely forget that the structure of all living
things is, as a whole, adaptive, and that a knowledge of how the
present forms come to be what they are includes a knowledge of why
they survived. They forget that the SUMMATION of variations on which
divergence depends is under the rule of the environment considered as
a selective force. They forget that the scientific study of the
interdependence of organisms is only possible through a knowledge of the
machinery of the units. And that, therefore, the investigation of such
widely interesting subjects as extinction and distribution must include
a knowledge of function. It is only those who follow this line of
work who get to see the importance of minute points of structure and
understand as my father did even in 1842, as shown in his sketch of the
"Origin" (Now being prepared for publication.), that every grain of sand
counts for something in the balance. Much that is confidently stated
about the uselessness of different organs would never have been
written if the naturalist spirit were commoner nowadays. This spirit
is strikingly shown in my father's work on the movements of plants. The
circumstance that botanists had not, as a class, realised the interest
of the subject accounts for the fact that he was able to gather such a
rich harvest of results from such a familiar object as a twining plant.
The subject had been investigated by H. von Mohl, Palm, and Dutrochet,
but they failed not only to master the problem but (which here concerns
us) to give the absorbing interest of Darwin's book to what they
discovered.

His work on climbing plants was his first sustained piece of work on the
physiology of movement, and he remarks in 1864: "This has been new sort
of work for me." ("Life and Letters", III. page 315. He had, however,
made a beginning on the movements of Drosera.) He goes on to remark with
something of surprise, "I have been pleased to find what a capital guide
for observations a full conviction of the change of species is."

It was this point of view that enabled him to develop a broad conception
of