1849.] 



exercised by Trees on Climate. 



415 



of the water tliat falls from heaven ; plants which grow in very 

 liot and very dry situations sometimes have the entire stem and 

 leaf transformed into a channel ; such is the aloe of the island of 

 Socotora at the entrance of the !Red Sea or the prickly taper of 

 the torrid zone. The aqueduct of the former is horizontal, and 

 that of the latter perpendicular. 



Wliat has prevented botanists from remarking the relations 

 that exist between the leaves of plants and the waters by which 

 they are refreshed is that they see them every where nearly of the 

 same form, in the vallies as on the eminences: but though the 

 mountain plants exhibit foliage of every species of configuration it 

 may be easily perceived from their aggregation in the form of hair 

 pencils or of fans, from the contraction of the leaves or other equi- 

 valent marks, but principally from the aqueduct which I have just 

 mentioned, that they are intended to receive the rain water. This 

 aqueduct is traced on the stalk of the smallest leaves of mountain 

 plants ; it is by means of it that nature has rendered even the 

 forms of aquatic plants susceptible of vegetation in the most 

 parched situations. The reed for example, which is only a round 

 ftdl pipe that grows by the water-side, appears incapable of collect- 

 ing any humidity in the air though it is well adapted to elevated 

 situations by its capillacious form which like that of gramineous 

 plants, presents nothing which the wind can lay hold of. In fact 

 if you examine the different species of the rush that clothe the 

 mountains in various parts of the world, such as that called icho, 

 on the lofty mountains of Peru, which is the only vegetable that 

 grows on some parts of them, and those that thrive in our climates 

 in parched sands or on eminences, you would, at first sight, believe 

 them to be similar f!b the rush of the marshes : but a little atten- 

 tion will enable you to observe, not without astonishment, that 

 they are hollowed into a gutter throughout their whole length. 

 Like other rushes, they are convex on one side : but they differ 

 from them essentially in being concave on the other. By this 

 character I discovered the spart, which is a rush of the mountains 

 of Spain and is now employed at Taris to make cordage for draw 

 wells. 



The leaves of many plants, even in the plains, assume on their 

 firyt appearance this form of a gutter or spoon^ as those of the 



