524 THE POPULAR SCIENCE MONTHLY. 



periments in which this species, with Helix hortensis and Limax 

 agrestis, a voracious all-feeder, were put in presence of several 

 plants having strong odors and pronounced flavors, showed that 

 their tastes as toward living plants were very different. These 

 experiments tend to show that the living plants are protected to 

 a greater or less extent by the presence of some constituent disa- 

 greeable to the snails, which we may regard as a defensive armor 

 to them. The dead parts of the plants were preferred, although 

 as a rule dried vegetable is less alimentary than fresh, because 

 the disagreeable substance had been removed or weakened by 

 evaporation. Other experiments show that this kind of armor is, 

 as a rule, the most effective. 



When a drop of the juice of sorrel, garlic, saxifrage, or nastur- 

 tion is put upon the tegument of a snail, the animal manifests 

 pain and exudes abundance of its mucous secretion ; yet it is not 

 thus affected by a drop of water. When snails avoid plants 

 marked by such juices, we have a right to regard the plants as 

 defended by a chemical armor. The offensive substance may also 

 be important to the nutrition of the plant, but that is not the ques- 

 tion we are dealing with here. Many plants are evidently lacking 

 in this means of defense ; for, of some plants, all the animals ex- 

 perimented upon have been found to prefer fresh to dead parts. 

 Others are never touched by them, whether living or dead. Hence 

 we may conceive that an infinite variety may exist in the degrees 

 of chemical armoring between total absence of protection and 

 complete protection. 



Plants containing perceptible tannin are disagreeable to nearly 

 all animals. Only swine will eat acorns as if they regard them 

 as food. Other animals reject them, except when they can not get 

 anything else. Leguminous plants containing tannin in weak 

 proportions are eaten by horses and cattle, but snails are not fond 

 of them. But the garden snail, which lets fresh clover alone, will 

 eat it freely after the tannin has been extracted with alcohol. 

 It is also probably tannin that inspires snails with respect for 

 vetches, saxifrage, and stone-crop. Many water-plants, likewise, 

 strong in tannin, are respected by water-snails, while the treat- 

 ment with alcohol converts them into savory dishes for the same 

 animals. Other plants,' like dock, sorrel, and begonia, contain 

 oxalic acid in notable quantities, and are obnoxious to them when 

 too freely mixed with their food. It is worthy of remark that if 

 carrot, of which snails are fond, is soaked in solutions of tannin 

 or oxalic acid, they will avoid it in proportion as it is strongly 

 impregnated with the offensive substance. 



Strongly acid substances are often found on the surface of the 

 leaves of plants. M. Stahl casually perceived that a leaf of (Eno- 

 thera caused a very pronounced acid sensation on contact with 



