252 HOW CROPS GROW. 



Soil-Roots: Water-Roots J Air-Roots, We may dis- 

 tinguish, according to the medium in which they are formed 

 and grow, three kinds of roots, viz. : soil-roots, water-roots, 

 and air-roots. 



Most agricultural plants, and indeed by far the greater 

 number of all plants found in temperate climates, have 

 roots adapted exclusively to the soil, and which perish by 

 drying, if long exposed to air, or rot, if immersed for a 

 time in water. 



Many aquatic plants, on the other hand, die if their 

 roots be removed from water, or from earth saturated 

 with water. 



Air-roots are not common except among tropical plants. 

 Indian corn, however, often throws out roots from the 

 lower joints of the stem, which extend through the air 

 several inches before they reach the soil. The Banyan of 

 India sends out roots from its branches, which penetrate 

 the earth in like manner. Many tropical plants, especially 

 of the tribe of Orchids, emit roots which hang free in the 

 air, and never come in contact with water or soil. 



A plant, known to botanists as the Zamia spiralis, not 

 only throws out air-roots, c c, Fig. 44, from the crown of 

 the main soil-root, but the side rootlets, #, after extending 

 some distance horizontally in the soil, send from the same 

 point, roots downward and upward, the latter of which, 

 d, pass into and remain permanently in the air. A is the 

 stem of the plant. (Schacht, Anatomie der Gewdchse, Bd. 

 II, p. 151.) 



Some plants have roots which are equally able to exist 

 and perform their functions, whether in the soil or sub- 

 merged in water. Many forms of vegetation found in 

 our swamps and marshes are of this kind. Of agricul- 

 tural plants, rice is an example in point. liice will grow 

 in a soil of ordinary character, in respect of moisture, as 

 the upland cotton-soils, or even the pine-barrens of the 

 Carolinas. It flourishes admirably in the tide swamps of 



