PLANTS ADAPTED TO ABSORB GASES 436 



Plants Adapted to Absorb Gases, Water, and Salts. 

 — Since these raw materials are absorbed through the 

 leaves and roots it follows that the former must be 

 properly exposed to the air and the latter to the soil. 

 Leaves must not only absorb oxygen from the air and 

 discharge carbon dioxid into it in the dark but they must 

 also reverse this order in sunlight and absorb carbon 

 dioxid and light energy and discharge oxygen. To do 

 this efficiently requires many shapes and positions of 

 leaves. 



The roots likewise present a wide range of variation. 

 Primarily they are adapted to absorb water and dissolved 

 salts anywhere from the surface of the earth to a depth of 

 at least seventy-five feet, in the case of certain desert 

 species. At the same time it is highly important that 

 they function as holdfasts to anchor the plant in a secure 

 position. 



In parasitic species, such as the mistletoe and dodder 

 (Chap. XVIII) specially adapted roots serve to absorb 

 nutritive materials from the host plant. In many lower 

 species of plants, such as fungi and bacteria, the individ- 

 ual is fitted to decompose and absorb organic sub- 

 stances. Still other species, ranging from relatively simple 

 to highly complex types, are adapted to an aquatic life 

 where delicate tissues, few if any roots, but a highly de- 

 veloped absorbing body surface are the more general 

 adaptations. 



Insectivorous Plants. — Several species of flowering 

 plants have been described which add to their customary 

 food supply the digested remains of animals, chiefly in- 

 sects, and in this way are adapted to a life in soils poor 

 in nitrogen. In the pitcher plant, which affords a good 

 example, the leaves are slender vase-shaped structures 

 whose rims secrete a sweet fluid which slowly oozes down 

 their outer surfaces. In the interior, immediately below 

 the rim is a smooth slippery zone; beneath this there 

 is a second zone provided with inwardly directed hairs; 



