106 ORGANS AND FUNCTIONS OF. PLANTS. 



laurel, must be retained in separate vessels, for when 

 introduced into the plant through the roots, they act 

 as poisons, and kill the very plants in which they had 

 been secreted, in the same way as the poison from the 

 sting of a bee, or from the fang of a serpent, will kill 

 those animals. 



ORGANS OF SENSATION. 



DR. DARWIN fancied plants to be endowed not 

 only with feelings, but with sentiment and passion ; 

 and more recently Dutrochet has attempted to demon- 

 strate the existence of nervous organs in plants, at 

 least in the sensitive plant, so well known for the sin- 

 gularity of closing and dropping its leaves when they 

 are touched, or deprived of light, even by the shadow 

 of a passing cloud. At the base of the leaf-stalk 

 of this plant is a sort of bulging collar, composed of 

 a delicate tissue of cells, upon which the motion of 

 the leaf depends ; for when the under part is cut 

 away, the leaf remains bent down, and cannot again 

 erect itself; and when the upper part, it cannot bend 

 down; so that the collar obviously consists of two 

 antagonist springs, set in motion, not by what he 

 terms nervous globules a sort of grains of a green 

 colour diffused through the textures of plants but, 

 strange to say, by the vessels forming the pith tube. 



That the irritability, as it is termed, of the sensitive 

 plant, depends upon the carbon which it contains, or 

 upon its due proportion of pulp, appears from its losing 

 this irritability in the dark. Professor Burnet, from 



