IRRITABILITY OF VEGETABLES. \$g 



tuved, at that time; though not so quickly as the lettuce, 

 or with the same facility and force. It requires a stronger 

 irritation, or a more powerful and complex stimulus, to 

 excite the flow of the milky liquid in' this plant; and does 

 not obey the slightest touch like the lettuce, which, as 

 soon as it is touched, however gently, throws out a portion 

 «>f its proper or milky juice. 



This exudation is never performed with the same force and more strip 

 as in the lettuce, from which it is sometimes spirted out ^"^ e In the 

 into the air to some distance ; but simply flows out, 

 however powerful the irritation. Neither is it obtainable 

 from the leaves that embrace the stalk, as in the lettuce, 

 but from the calices alone, and chiefly from the circum- 

 ferences of the little leaves that compose these. 



The sowthistle, like the lettuce, does not lose this faculty Not destroyed 



when immersed in water; and the plant, if pulled out oi' b y >mmersioa 



. . . in water, 



the ground, or a single branch of it, will retain it some time. 



I have not had time to extend my observations to the Found in the 

 other species of the lettuce end sowthistle, to find whether, P encar P- 

 either while flowering or at any other time, they gave 

 signs of a sensible degree of irritability in any part by a 

 similar exudation, though this is probable, I have found, 

 it in the bark of the fruit when green, or in the pericarps 

 of these plants. 



I could not obtain the customary exudation from the other parts 

 leaves, the stalks, the parts that support the organs of void of it. 

 fructification, or any other part, in whatever way I irritated, 

 them, except from the green capsules containing the 

 seeds : and the irritation was always produced by a needle, How excited. 

 or rubbing; never by any method capable of tearing or 

 injuring the surface of the capsules*. 



* There are motions in plants not owing to irritability, but the jL e mu j] e ; n 

 simple effects of the elasticity of certain parts, as in the great mullein made to shed 

 (verbascum sinnatum). If a shock, or commotion, be given to the its flowers.' 

 stalk of this plant, the flowers will fall off; not immediately, nor all 

 at once, but a little while after, and successively. This is owing to 

 the elasticity of the calices, which are kept in a state of forced dis- 

 tension to hold the monopetalous flower, which is not attached to 

 them ; and as the shock causes them to contract, by calling inte 

 action th«ir natural elasticity, this contraction gradually expels the 

 flower. 



lfind 



