THE DEFENSIVE ARMOR OF PLANTS. 525 



the tongue, which was due to the presence of a superficial acid. 

 On examination he found the same property present in other 

 plants of the Onogracecz and Papilionacecz. The acid is secreted 

 by numerous one-celled cylindrical hairs. It consists of a mixt- 

 ure of oxalic, acetic, and malic acids, and, being very disagreeable 

 to slugs and snails, constitutes an efficacious protection against 

 their ravages. A simple contact of its tentacles or teguments 

 with the secretory hairs is enough to cause the animal to draw 

 back and go somewhere else to indulge its cravings. But if the 

 leaves are washed, and the hairs cleansed of the acid secretion, 

 they will be eaten at once. 



Many plants are furnished with strong and pungent ethereal 

 oils or similar substances. Prof. Tyndall thinks that these es- 

 sences help to protect the plant against excessive heat. With- 

 out disputing this, M. Stahl finds that they are also efficient in 

 defense against animals. This was proved with respect to rue, 

 calamus, peppermint, dictamnus, and crane's-bill ; and snails would 

 at once turn out of the way to avoid a crushed leaf of the latter 

 when placed in their road. Bitter leaves were avoided when fresh ; 

 when dead, even those of the gentian were relished, although the 

 fresh ones were rejected by very hungry animals. The expressed 

 juices were very disagreeable to them. The bitter was evidently 

 the unpleasant quality, for the plants in question were free from 

 tannin.* The liverworts, according to W. Pfeffer's researches, con- 

 tain fat substances, the function of which is unknown, but to 

 which Mr. Stahl ascribes a protecting agency. It is certain that, 

 though they are easily accessible to all animals, they very rarely 

 present any traces of having been attacked by them ; and land- 

 snails respect them in a very marked manner. Even after four- 

 teen days of fasting, Helix hortensis could not resolve to eat the 

 thallus of Pellia. But there are genera (L/unaria and Marchantia) 

 of which the less delicate snails will consent to eat a little. When 

 the thalluses are treated with alcohol, the mollusks accept them 

 readily ; and there are some, like Plagiocliila, that they will even 

 eat fresh, in spite of their disagreeable smell, because of the much 

 sugar that is in them. But most plants of the order are avoided, 

 because of the unpleasant taste and smell given them by their 



* 51. Stahl did not particularly concern himself with alkaloids, although they must 

 have played a considerable part in defense in some of the plants that he experimented 

 with. On this point we may refer to some of M. Errera's conclusions, as given in the 

 paper of himself and Maistrian and Clautrian (Brussels, 1887) on the "Localization and 

 Importance of Alkaloids in Plants " : " The alkaloids can hardly be regarded as other than 

 the waste of protoplasmic activity. In fact, it has been proved by experiment that they 

 can not serve as nitrogenous food to plants, and are toxic even to the plant that produces 

 them. . . . The recent researches of Armand Gautier in the ( anirnal kingdom bring a strong 

 confirmation to these views. It may be said that a few grammes of an alkaloid protect 

 a plant against the devastations of animals as effectually as the strongest thorns." 



