528 THE POPULAR SCIENCE MONTHLY. 



mies against which a plant has to contend to maintain its exist- 

 ence, their defenses are more numerous than we would suspect, 

 and more important than we might at first believe. 



In analyzing M. Stahl's results, we perceive that some families 

 possess, as a whole, similar methods of protection: the grasses, 

 sedges, and horse-tails, silicification ; the rough-leaved orders, 

 hairs ; the Amaryllidece,, Asparagem, orchids, and Onagracece, ra- 

 phides ; the gentians, bitter substance ; the rose family, geraniums, 

 legumes, and heaths, tannic acid ; the nightshades, alkaloids ; the 

 labiates, ethereal oils; mosses, mechanical means (by silicifica- 

 tion) ; and liverworts, chemical means, and one genus of them, 

 Biccia, mechanical means also. 



Different genera in the same family sometimes present quite 

 diverse means. Among the lilies are genera (Scitta and Ornifho- 

 gallus) having raphides ; others, alliaceous compounds ; lilies, tu- 

 lips, and crown imperial, poisons. There are also differences be- 

 tween the species of the same genus ; thus, one species of Sedum is 

 protected by tannin, and another by an alkaloid. And in the same 

 plant there are often very notable differences between the leaves, 

 fruit, and root. 



M. Stahl asserts that he has not found a single phanerogamous 

 species, living in a wild condition, that is not armed in some way 

 against slugs and snails. Such armor is wanting only among cul- 

 tivated plants, or, rather, among some of them. It appears as if 

 at the moment when man cultivates a species of plant, or takes 

 it under his protection, using all possible means to facilitate its 

 existence and remove its enemies, the plant gives up its own 

 means of maintaining the struggle, surrendering its defensive 

 armor at man's invitation. The common lettuce is a striking 

 example of this fact. It is a favorite viand, as all know, of the 

 Gasteropods of the garden. Nothing protects it against their 

 attacks, and its smooth, tender, and succulent leaves make it a 

 ready prey to them ; yet it is the descendant, modified by culti- 

 vation, of the Lactuca scariola, which has chemical constituents 

 so distasteful to snails, and so constant, that they will not eat it 

 even after it has been treated with alcohol. 



The defensive armor of plants is most frequently situated upon 

 their surface, or where the attack begins. This is particularly 

 the case with the mechanical weapons and such chemical ones as 

 tannin, special juices, etc. 



When we consider how varied are these armors of plants and 

 how generally spread they are among all the orders, and that 

 without them some species would not be able to exist, it is hard 

 to deny that there is some special adaptation in them, or to sup- 

 pose that they are merely accidental. The case is undoubtedly 

 one of natural selection ; and the fact that the protection is gained 



