392 The Movements of Plants 
seconds of stimulation. It was this fact, more than any other, that 
made him doubt the current explanation, viz. that the movement 
is due to unequal growth on the two sides of the tendril. The 
interesting work of Fitting! has shown, however, that the primary 
cause is not (as Darwin supposed) contraction on the concave, but an 
astonishingly rapid increase in growth-rate on the convex side. 
On the last page of Climbing Plants Darwin wrote: “It has 
often been vaguely asserted that plants are distinguished from 
animals by not having the power of movement. It should rather be 
said that plants acquire and display this power only when it is of 
some advantage to them.” 
He gradually came to realise the vividness and variety of 
vegetable life, and that a plant like an animal has capacities of 
behaving in different ways under different circumstances, in a 
manner that may be compared to the instinctive movements of 
animals. This point of view is expressed in well-known passages 
in the Power of Movement®. “It is impossible not to be struck 
with the resemblance between the...movements of plants and many 
of the actions performed unconsciously by the lower animals.’ And 
again, “It is hardly an exaggeration to say that the tip of the 
radicle...having the power of directing the movements of the adjoin- 
ing parts, acts like the brain of one of the lower animals; the brain 
being seated within the anterior end of the body, receiving impres- 
sions from the sense-organs, and directing the several movements.” 
The conception of a region of perception distinct from a region 
of movement is perhaps the most fruitful outcome of his work on the 
movements of plants. But many years before its publication, viz. 
in 1861, he had made out the wonderful fact that in the Orchid 
Catasetum® the projecting organs or antennae are sensitive to a 
touch, and transmit an influence “for more than one inch instan- 
taneously,’ which leads to the explosion or violent ejection of the 
pollinia. And as we have already seen a similar transmission of 
a stimulus was discovered by him in Sundew in 1860, so that in 1862 
he could write to Hooker*: “I cannot avoid the conclusion, that 
Drosera possesses matter at least in some degree analogous in con- 
stitution and function to nervous matter.” I propose in what follows 
to give some account of the observations on the transmission of 
stimuli given in the Power of Movement. It is impossible within 
the space at my command to give anything like a complete account 
of the matter, and I must necessarily omit all mention of much 
interesting work. One well-known experiment consisted in putting 
1 Pringsheim’s Jahrb. xxxvit1. 1903, p. 545. 
2 The Power of Movement in Plants, 1880, pp. 571—3. 
3 Life and Letters, 111. p. 268. 
4 Life and Letters, ut. p, 321. 
