450 PROTECTION OF GREEN LEAVES AGAINST ATTACKS OF ANIMALS. 



a portion of the old dead leaves, by dried-up structures of the previous year, in 

 tragacanth bushes and also in many caraganas, and generally in numerous other 

 plants, two things may be learned: first, that one and the same plant-member may 

 in the course of a year change its function; and secondly, that dead, withered 

 portions are often called upon to play an important part in the life of a plant. The 

 same thing is frequently observed in flowers and fruits. It often happens, for 

 example, that floral leaves, which originally served to allure insects and to protect 

 the pollen from moisture, are of use later on when dried, in the dissemination of 

 the fruits and seeds. In foliage-leaves, on the other hand, such a change of function 

 is comparatively rare, and is hardly ever observed except in the plants of steppes 

 and of the Mediterranean flora. 



It would naturally be expected that the protective contrivances required by the 

 green tissue against an excessive destruction by animals, would also exercise an 

 influence on the gregarious growth of plants as well as on the dwelling together and 

 distribution of plants and animals; and this is proved by numerous observations. 

 Let us suppose ourselves in a country where plants of a hundred diflferent kinds 

 grow up side by side. The shrubs, bushes, and herbs, mixed together, contain the 

 most diverse substances. Some abound in milky juices; others are as bitter as gall; 

 whilst others again taste frightfully sour or contain in their sap alkaloids, the 

 partaking of which would be deadly to many animals. Here is a plant armed with 

 stinging hairs; there from a bush radiate out innumerable spines; and again in 

 other places thistles rear their prickly leaves. The one prevents snails from eating 

 the foliage, the other caterpillars or grasshoppers; a third, goats; a fourth, horses, 

 &c. Let it be supposed that the country producing this rich vegetation is 

 temporarily quite shut ofl" from everything which creeps or flies. But now arrives 

 a numerous herd of some species of animal against whose attacks one portion of the 

 plants is protected as completely as possible, a second portion only partly, a third 

 not at all. What will be the consequence? The last will be wholly or partly 

 devoured, while the first will remain uninjured. If this is often repeated, at last 

 the one will vanish from the scene, while the other will develop in overwhelming 

 quantity. But in this manner the peculiar composition of vegetation in places 

 where grazing animals regularly appear is naturally explained. 



It must strike everyone who visits the Alps that in the neighbourhood of the 

 cow-chalets a luxuriant vegetation springs up from the richly-manured soil, very 

 tempting in appearance, but nevertheless left unattacked by the grazing animals. 

 The shepherds do not prevent the animals from eating of this luxuriant gi'owth; it 

 is not necessary, for instinctively they detest these plants. The bush consists 

 entirely of species which are poisonous or disagreeable to the animals, or which 

 when disturbed, wound them — viz. of Monkshood, Good King Henry, Nettle, and 

 Fuller's Thistle {Aconitum, Napellus, Chenopodium Bonus Henricus, Urtica 

 dioica, Cirsium spinosissimum), which are found together here, and have developed 

 so much the more vigorously, since the other species originally existing (wliich were 

 innocuous and undefended) have been long ago destroyed by the gi-azing animals. 



