J 5 OUT THE FOOD OF PLANTS. 



whatever it may be, is to be sought for in vegetable earth, 

 the produce of animal and vegetable substances decayed. 

 Many plants indeed require little or no earth for their ve- 

 getation, such as the numerous lichens and tragacanths, of 

 which genera the former were discovered by Saussnre on the 

 highest of the Alpine granite rocks. Tn lower situations 

 these form a soil for the genista, for the cistuses, and more 

 especially for rosemary and lavender, which abound on the 

 most elevated mountains of the Pyrenees. These again, 

 by their decay, form vegetable earth, in which the luxuriant 

 pine trees and the ilex grow. 



Valleys. This vegetable matter, being washed down into the val- 



lies, helps to form and to increase their soil to a considerable 

 depth, and to give them that fertility, which is not readily 

 exhausted. 



Soil composed When we analyse a soil, we never fail to find it composed 



©f earths trom Q r su l )S tances derived from a superior level. If the hills are 

 the hills, & ve- . .„ ■ f . . . 



getablfc or ani- quartsoze, calcareous, argillaceous, or magnesian, so is the 



mal matter. so jl ; n all the vallies which communicate with them. But 

 with these earths in a rich soil we tind a great proportion of 

 Vegetable matter, or of animal exuvire ; and as these are de- 

 ficient or abound, vegetation languishes, or is exceedingly 

 luxuriant. 



Mould. Good mould abounding with vegetable matters is com- 



monly of a dark colour, pulverises easily, and has therefore 

 what is called a mellow look ; but when exhausted or im- 

 poverished by frequent crops, the richest soil, such as I have 

 here described, becomes arid, of a lighter colour, compact, 



Some will bear and comparatively barren. In a maiden soil, or where every 



continual shower of rain brings down from more elevated regions a 

 quantity of vegetable matter, a succession of luxuriant crops 

 may bte taken incessantly, without any diminution of fer- 

 tility. Thus it is in the country newly occupied by the 

 Americans, hi Kentucky, on the Ohio, and in the whole ex- 

 tent of territory watered by the Mississippi, or by its tribu- 

 tary streams. Thus- also in some parts of Spain, where an 

 extensive plain happens to receive the spoils of rich circum- 

 jacent hills, as in the well-watered vale of Orihuela, near 

 Murcia, of which they say, " Let it rain or not rain, corn 

 ixever fails in Orihusla." Indeed, so productive is wheat in 



thit 



