262 HARMONIES OF VEGETATION. 



of water, reduced to vapour, and mixed with other principles, 

 capable of solution and evaporation. 



VITALITY OF PLANTS. 



26. That plants are possessed of a living principle, 

 the previous essays on germination, food, nourishment 

 and functions, unite to convince us. The point is 

 further proved by the excitability, irritability and ap- 

 parent sensation and instinct, which some plants in par 

 ticnlar evince. 



27. By excitability is meant the capacity of a plant 

 being acted upon by the application of natural causes, 

 impelling it to the exertion of its vegetative powers. 



The most effectual sources or stimulants to display the excita- 

 bility of plants, are beat and light. By the former the germination 

 and developement is more or less brought about ; and from the latter, 

 the position, colour, and vigour of the individual, is in part derived. 



28. Vegetables are not only acted upon by the natural 

 causes we have alluded to ; they are susceptible also to 

 the influence of a variety of accidental or artificial stimu- 

 lants, from the application of which they evince a pro- 

 perty of irritability . 



This property is well exemplified in that species of mimosa known 

 by the name of the stntitict plant. If a leuflet of this plant is but 

 touched, however slightly, by any extraneous body, it immediately 

 shrinks into itself, and communicates the impulse, if strong, perhaps 

 to the whole wing, each pair of leaflets colapsing in succession, and 

 the leaf-stalk itself sinking downwards as if by a joint at its point of 

 union with the stem Illustrations of iritability are also met with in 

 the leaves of Venus'* fly-trap, and species of sun-dew ; in the 



