264 



The author's 

 definition of 

 the term. 



Plants experi- 

 mented on by 

 the author. 



Leaves of 

 rouarlieaved 

 sundew dd- 

 sciibed. 



ON THE IRRITABILITY OF VEGETABLES. 



the motions of plants may still be owing to irritability, al- 

 though there is no mind to regulate them? I do not mean 

 here to say, that plants have not a voluntary power; but 

 merely admit that they have not in the present question. 

 Wildenouw, when treating of the powers which vegetables 

 possess, sneaks thus on the subject. " Irritability, when 

 " different stimuli produce a change in the parts of a body, 

 " which without it would not have taken place*." 



The following definition seems to me as comprehensive 

 and accurate as any, and shows the meaning in which the 

 word irritability is used in the following pages. By irrita- 

 bility then I understand that property inherent in some 

 bodies, (or rather parts of bodies) by which, when a stimu- 

 lus is applied, they are enabled to contract. 



Having thus fixed the definition, let us proceed to the im- 

 mediate subject of the paper. The plants on which I made 

 my experiments were the drosera rotundifulia and lougifoba, 

 the euphorbia helioscopia, and the dionosa muscipula. The 

 species of drosesa come first under consideration; but before 

 speaking of the moving power of their leaves, I think it ne- 

 cessary to give a minute description of them : and 1st of the 

 votundifolia. 



The leaves of this plant, when properly unfolded, lie round 

 the stem in a stellated manner. The footstalks of the leaves 

 vary in length from half an inch to one inch and half. On 

 the upper side they are a little roundish, and have at the 

 same time a two edged appearance. The under surface is 

 quite fiat, and bounded by the two edges' just mentioned. 

 They are of a reddish colour, and are covered by a great 

 number of long white hairs, spreading in different direc- 

 tions. They may be bent considerably without breaking, . 

 and, when the resisting force is removed, resume their for- 

 mer situation. At the end of the footstalks we find the 

 leaves generally of an orbicular shape, hence the specific 

 name of the plant. The under surface of the leaf is in the 

 same plane with "the under surface of the footstalk, (indeed 

 it is difficult to say where the one ends and the other begins) 

 lias a somewhat membranaceous appearance, and is in gene- 

 ral of a greenish (though sometimes purplish) colour. The 



* Principl. Botany & Vcg. Physiol. Wildenow (Translat. p, 219.) 



upper 



