Royal Institution of Great Britain* 435 



anticipated by Lindsay, but each pursued the inquiries with a dif- 

 ferent view, and partly in a different course. 



The result of these collateral experiments had been to prove, that 

 the tuber at the articulation of each leaf with the stalk, is formed 

 by antagonist elastic springs, the superior serving to depress, the in- 

 ferior to elevate the leaf; for if the upper part of the intumescence 

 be cut through, the leaf rises more than natural, and no irritation, 

 however violent, can cause it to collapse ; that if the under part be di- 

 vided, the leaf falls, and by no extent of rest will it again be enabled 

 to rise ; also the lateral parts being cut, a lateral flexion is caused 

 towards the wounded side. 



Similarly acting organs exist at the articulations of the pinnules, 

 and of the leaflets, only in the one case they are placed laterally, and 

 in the other diametrically opposite to their position on the leafstalk ; 

 their motions are in accordance with this change of place, and by 

 similar operations may be interrupted. 



Experiments were performed to show what would ensue from the 

 isolation of different parts ; branches, leaves, leaflets, &c., were en- 

 tirely removed from the plants, and yet their motive powers re- 

 mained ; the pinnules were separated from each other by longitu- 

 dinal and transverse incisions, and the leaflets on each side of a 

 pinnule separated by a long incision, by which the course and the 

 progress of the irritation could be traced. The under sides of seve- 

 ral leaves and leaflets were blackened, and by thus preventing the 

 access of light, the collapse became greatly prolonged ; from these 

 and other experiments, the following conclusions may be drawn : 



1. That plants possess motility. 



2. Tiiat the motive power is resident in each part, independent 

 of its communion with the rest of the plant. 



3. That although a connexion may exist, for the performance of 

 these motions, no communication with any common centre is re- 

 quired. 



4. That there is no evidence of any structure similar to what may 

 be truly called a nervous system in animals ; and that if any system 

 analogous exist, it must be in a very rudimental state. 



5. That plants are destitute of sensation and volition, i. e. there is 

 no such thing as " perceptivity" among vegetables. 



The perceptivity of plants has been inferred, and a nervous system 

 presumed to exist, from certain curious phenomena, as the course 

 of the radicle and plumula, the direction of roots, the climbing of 

 voluble stems, the increase and loss of defensive armour in prickly 

 and thorny shrubs, &c. &c. which may better be explained as the 



