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 1 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 4 : " 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. xxxviii. 1903, p. 545. 



8 The Power of Movement in Plants, 1880, pp. 571—3. 



3 Life and Letters, in. p. 268. 



4 Life and Letters, in. p. 321. 



