252 HOW CROPS GROW. 
Soil-Roots; Water-Roots: Air-Roots,x—We may dis- 
tinguish, according to the medium in which they are formed 
and grow, three kinds of roots, viz.: sodl-roots, water-roots, 
and aér-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, ¢ ¢, Fig. 44, from the crown of 
the main soil-root, but the side rootlets, d, after extending 
some distance horizontally in the soil, send from the same 
point, reots 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. Rice 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 
