THE MEANS Of SELI-PROTECTION POSSESSED BY PLANTS. 233 
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evident to every one that a large starchy tuber would stand a very 
poor chance of escaping destruction during the many months it has 
to remain just beneath the surface of the ground awaiting the next 
rainy season, were it not that nature affords a sufficient protection 
by storing in the root-cells a number of needle-shaped ’ crystals 
which cause the most intense irritation when ingested by any 
animal, and have often proved fatal to man. ‘The effects produced 
by the raw or imperfectly cooked plant are swelling of the tongue 
and throat, convulsions, asphyxia, and other signs of poisoning by 
an irritant. 
Pedler and Warden in 1886 were the first to point out that the 
toxic effects of Kachoo (the Bengal name for Colocasia) were due to 
entirely mechanical causes, and that the tubers contained no specific 
organic poisonous principle as had hitherto been supposed. 
The same theory has since, apparently, been independently adopted 
by Herr Stahl, who, at arecent meeting of the Jena Naturalists 
Society, read a paper upon the significance of those excreta of plants 
which are known asraphides. From experiments this investigator 
inferred that they were a protection to plants against being eaten 
by animals. Many animals avoid plants with raphides, or eat them 
reluctantly, and snails in eating these plants select those parts 
which are without the crystals. (Nature, Dec. 29th, 1887.) 
Messrs. Pedler and Warden’s experiments showed that these 
needle-shaped crystals are composed of calcic oxalate, a salt very 
insoluble in water even after moderate boiling, which accounts for 
the acridity of the tubers when cooked in the ordinary manner ; 
they also demonstrated that the addition of nitric and hydrochloric 
acids, which dissolve the salt, immediately removes the acridity of 
the tubers. Two difficulties still remained—Ilst, it is well known 
that the dried tuber is practically harmless, but microscopic exami- 
nation explained this by showing that the crystals, which in the 
fresh root are arranged in loose fan-like bundles, are in the dried 
root brought parallel to one another and become adherent, forming 
practically a single blunt crystal; 2nd, how is it that the hydro- 
chloric acid of the gastric juice does not dissolve the crystals: and 
thus prevent irritation of the intestines ? The answer is that excessive 
irritation of the stomach procuces a stoppage of the flow of gastric 
juice, and the pouring out of a ropy mucus instead. (See Pedler 
and Warden’s paper, Journ. Asiat. Soc. of Bengal, Vol. LVII., Part 
II., N., 1, 1888.) When cooking these plants the natives of India 
