IRRITABILITY OF VEGETABLES. 14 | 



I immersed lettuce plants in some stagnant water, from Lettuce im- 

 which fetid exhalations rose, and kept th. m to it twenty- ™ a e n ^ t ^ 8 " 

 four hours. Having taken them out, a d repeatedly ex- 

 amined the state of their irritability by stimuli, 1 found 

 they had lost it entirely. The vessels containing the 

 proper juice of the plants were so deprived of irritability, 

 that they did not emit their fl'i.d, even though wounds 

 were made in the plants for the purpose. It seems there- 

 fore, that putrid exhalations, or putrid matter combined 

 with water, deprive these plants, as well as animals, 'of 

 their irritablity. 



Having taken a lettuce plant, when Reaumur's ther- JJW - toa 

 mometer was at 25° in the shade [88*25° F.], t immersed ° 

 it in water at 50° [144'5° F.] ; a degree of heat I had found 

 not to injure the organic texture of vegetables. In this 

 hot fluid there was a spontaneous exudation from the 

 • plant; and at the slightest touch it gave out its juice more 

 freely than in air at the same temperature. I then im- and Iow teno 

 mersed it for a moment in water at 4* [41° F.]; and, after pera ure * 

 waiting for a few seconds, that it might have become 

 sensible of the effect, I irritated it afresh ; when I found it 

 required a much stronger irritation. 



The irritability of vegetables appears to be increased by Irritability of 

 heat, and diminished by cold. Vegetables in fact slacken ^^sed b^heat 

 in the exercise of their functions, if they do not suspend it and dimissish- 

 entirely, during the cold weather; and the spring, which 5 

 brings with it warmth, restores to the vegetable economy its 

 accustomed energy. By this it appears their sleeping irrita- 

 bility is awakened, and their life revived ; so that the state, 

 in which vegetables pass the winter, may be compared with 

 the torpor, or lethargy, that many animals undergo during 

 that season. Cold benumbs animals, because as is well 

 known, it deadens their irritability; and this it does by its 

 direct action on the muscular fibre, which is the seat of 

 irritability, independent of sensation and circulation, as 

 Spallanzani has shown. 



Into a deep well, where the thermometer was at 32° [59° A moderate 



F.1, 1 put a plant of lettuce in full flower; taking it from a temperature 

 r. 6 does not affect 



kitchen garden, where the thermometer stood at 26° [90*5° F.] it. 



in the shade : and kept it there some hours, with its root only 



