PECULIAR JUICES. 97 



independent of those operations ; and it is sleeping or 

 waking, whether in the daytime or the night, that the 

 difference I mentioned has been observed. 



Besides the water which plants exhale from the leaves, 

 there are several peculiar juices elaborated by glands sit- 

 uated on the surface of the leaves. These are furnished 

 with hairs, at either the point or base of which they grow, 

 and may be compared to the hairs which grow at the 

 orifice of the pores of our skin. 



Emily. How extremely minute must those glands be 

 which can be supported on so slender and frail a stem ! 



Mrs. B. You may thence form some idea of the di- 

 minutive size of the vegetable organs in general. When 

 the secretory gland is situated on the summit of the hair, 

 the liquid it secretes is of an innocent nature ; but when 

 situated at the base, the secretion is acrid, caustic, and 

 poisonous. 



Caroline. This is, no doubt, ^the case with nettles, 

 which pour their poisonous secretions on the skin, and 

 raise it into blisters. 



Mrs. B. The poison must penetrate beneath the cu- 

 ticle in order to produce this effect ; the hair is the instru- 

 ment which gives the wound, and the poisonous juice is 

 then poured into it. 



Emily. This is just like the sting of a serpent, who 

 inflicts a wound and then ejects his poison into it. But 

 what is the reason that nettles do not sting when wet- 

 ted with rain ? 



Mrs. B. Because the hair, when softened by mois- 

 ture, has not sufficient strength to perforate the skin ; 

 and, unless a puncture be made, the secretion cannot in- 

 sinuate itself beneath the skin, and no sting is felt. 

 Stinging plants can also be handled with impunity after 

 death, if dried, for, though in this case the instrument 

 may be capable of wounding, the poisonous juice is no 

 longer fluid, and cannot flow into the puncture. 



536. Why may it not be owing to plants giving out oxygen during the 

 day, and absorbing it during the night 1 537. With what are the 

 glands situated on the surface of the leaves furnished, and what is said of 

 them] 538. What is the difference in the liquid secreted, whether it 

 be from the summit or the base of the hair! 539. In what manner 

 are nettles able to produce such effects, when applied to one's flesh 1 

 540. Why are not nettles able to sting when wetted with rain! 541. 

 What is said of stinging plants when deadl 

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