CHAP. XV. 
IRRITABILITY. 
419 
the experiments with vegetable poisons, the Bean plants were 
carefully taken from the earth, and their roots immersed in 
the solutions used. It had been previously ascertained, that 
plants so transplanted and placed in water, under ordinary 
circumstances, would remain in excellent health for six or 
eight days, and continue to vegetate as if in the earth. A 
plant was put into a solution of nux vomica at nine in the 
morning: at ten o’clock the plant seemed unhealthy; at one 
the petioles were all bent in the middle ; and in the evening 
the plant was dead. Ten grains of an extract of cocculus 
suberosus, dissolved in two ounces of water, destroyed a 
Bean plant in twenty-four hours ; prussic acid produced 
death in twelve hours, laurel water in six or seven hours, a 
solution of belladonna in four days, alcohol in twelve hours. 
From the whole of his experiments, M. Marcet concludes, 
— 1st, That metallic poisons act upon vegetables nearly as 
they do upon animals : they appear to be absorbed and car- 
ried into different parts of a plant, altering and destroying 
the vessels by corrosive powers. 2dly, That vegetable poi- 
sons, especially those which have been proved to destroy ani- 
mals by their action upon the nervous system, also cause the 
death of plants : whence he infers that there exists in the 
latter a system of organs which is affected by poisons, nearly 
as the nervous system of animals. 
These facts have been confirmed by other experiments of 
Macaire, which will be mentioned presently. 
Irritability, in the common acceptation of the term in bo- 
tany, means those extreme cases of excitability in which an 
organ exhibits movements altogether different from those we 
commonly meet with in plants. Of this kind of irritability 
there are three distinct classes ; namely, those which depend 
upon atmospheric phenomena, spontaneous motions, and such 
as are caused by the touch of other bodies. 
Among the cases of irritability excited by particular states 
of the atmosphere, the singular phenomenon called by Lin- 
naeus the sleep of plants is the most remarkable. In plants 
with compound leaves, the leaflets fold together, while the 
petiole is recurved, at the approach of night ; and the leaflets 
again expand and raise themselves at the return of day. 
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