Water y i 



largest they are so minute as entirely to exclude the very 

 finest dust. Those of the white Uly, for instance, which 

 are called * 'remarkably large," measure only one four 

 thousand two hundred and fiftieth part of an inch across. 



Hard, evergreen leaves, such as those of the pine, are 

 like the thick, fleshy ones in this, that they have but few 

 leaf-pores, and lose but little water except through these 

 openings. For pines grow in very dry, sandy soils, and 

 often in elevated situations, where the air, though cold, is 

 exceedingly dry and drying, and they therefore need 

 as much protection as plants which grow in hot, dry 

 climates. 



Many and various are the devices by which evapora- 

 tion is checked and controlled, even in temperate latitudes, 

 lest the plant's need of water should exceed the supply. 

 For it must be remembered that air has an immense appe- 

 tite for water; the drier it is the more it takes up, but 

 it goes on sucking, if allowed, as long as it is in contact 

 with anything containing moisture until it can hold no 

 more. 



It is this which makes the miseiy of an east wind, 

 which is a very dry wind, as well as a cold one, and sucks 

 up moisture wherever it can, not only from vegetation, 

 but from the bodies of animals, drying the skins of human 

 beings as the hot, dry air of the desert dries them, though 

 in less degree. 



Since three-fourths of the weight of most plants, and 

 more of many, is made up of water, the air would be 

 always sucking at them, if not prevented. As things are, 

 however, though some, generally very small, amount of 

 water is sucked by the air from the whole surface of a 

 plant, as we have said, its escape is confined, as far as 



