The Botanical Work of Darwin . xvii 
His views on aggregation have been shown to be incorrect, 
but remain as the starting-point of a curious subject. The 
work on insectivorous plants is, however, more remarkable 
for the boldness and originality of the central idea of the 
book than for anything else. As he has said, ‘ The fact that 
a plant should secrete, when properly excited, a fluid con- 
taining an acid and ferment, closely analogous to the digestive 
fluid of an animal, was certainly a remarkable discovery V 
In his book on Climbing Plants he wrote : — ‘ The conclusion 
is forced on our minds that the capacity of revolving, on 
which most climbers depend, is inherent, though undeveloped, 
in almost every plant in the vegetable kingdom 2 .’ This, 
extended and modified, forms the central conception of his 
book on the Power of Movement in Plants, 1880. He 
showed that circumnutation is a widely spread phenomenon, 
that practically all plants carry on their growth in a rhythmic 
manner, which is identical on a small scale with the revolving 
nutation of climbing plants. But, as is well known, he went 
much farther than this, and attempted to prove that the 
movements of plants have been evolved by various modifica- 
tions of circumnutation. It is a point of view which harmo- 
nizes admirably with his evolutionary views, namely, the 
conception of a plant attaining an adaptive movement (e. g. 
geotropism) by selection from a tentative series of move- 
ments — in a way that calls to mind the selection and summa- 
tion in a given direction of morphological variation. This 
view has not been accepted by botanists, and personally 
I doubt whether it should be accepted in the form in which 
it is stated ; for I doubt whether we know enough of the 
machinery of curvature, as distinct from the machinery of 
rectilinear growth, to understand the connexion between the 
two. But, as Sir William Thiselton-Dyer has said, 4 No one 
can doubt the importance of what Mr. Darwin has done in 
showing that for the future the phenomena of plant movement 
can and indeed must be studied from a single point of view 3 .’ 
1 Life and Letters, Vol. i, p. 96. 2 Climbing Plants, p. 205. 
3 Charles Darwin, Nature Series, 1882, p. 41. 
b 
