THE DEFENSIVE ARMOR OF PLANTS. 523 



M. Stahl's experiments were made in his own garden and in the 

 woods in the neighborhood, and bore direct reference to the atti- 

 tude of snails toward the plants. The questions were asked, What 

 plants do snails prefer ; what ones do they avoid, and why do they 

 avoid them ? The results of his study may be verified by almost 

 any one. Several species of snails were observed ; including spe- 

 cial feeders, those which live wholly on mushrooms, and om- 

 nivorous snails, which, while preferring certain species, eat more 

 or less of all kinds of plants, and sometimes accommodate them- 

 selves to animal food. 



Pieces of mushroom were offered to the snails, a part of them 

 fresh, others after having been macerated in alcohol, dried by 

 evaporation, and washed. The different species varied in their 

 behavior toward the food. The omnivorous snails would not eat, 

 or would only touch the fresh pieces, but readily devoured those 

 which had been treated with alcohol ; but a special feeder ate the 

 fresh pieces and left the others. Hence the author concluded that 

 there exists in the fresh mushroom a substance soluble in alcohol 

 that attracts some animals and repels others. It must not, how- 

 ever, be believed that the special feeders can only live on particu- 

 lar food, for they are capable of accommodating themselves to 

 other kinds when it is necessary. That the ingredient soluble in 

 alcohol was the essential element of the food was proved by the 

 special feeders, which avoided the macerated and dried food, but 

 returned to it when it had been soaked again in the alcohol by 

 which that ingredient had been abstracted. 



Some light is cast upon the bearing of this experiment by 

 reflecting on the enormous quantities of food which the omnivo- 

 rous snails in a state of nature require. A vine-snail or a slug 

 will eat a quarter or a third of its weight of carrot or potato in 

 twelve or twenty-four hours. Although their needs are but slight, 

 they can hardly find enough to assuage their hunger, on account 

 of the mechanical or chemical defenses which most plants offer 

 against them. Thus, the garden snail causes immense destruction 

 of the filbert-leaves in the spring; but it would cause more if 

 these leaves did not contain certain chemical substances, for it 

 eats them more greedily after they have been treated with alco- 

 hol. Though this sort of protection is only relative, it will appear 

 very considerable when we reflect upon the abundance and fer- 

 tility of some species of snail. 



Examining a garden near Jena after a warm rain in April, 

 of forty-four snails of the species hortensis, fruticum, and arbus- 

 torum, ten were found upon living plants, while the thirty-four 

 others were eating dead leaves. These three species, therefore, 

 most usually attack dead plants. Helix pomatia, on the other 

 hand, was observed almost exclusively upon living species. Ex- 



