238 HOW CROPS GROW. 
upper portion of the tap-root of the beet, turnip, carrot, 
and radish, expands under cultivation, and becomes a 
fleshy, nutritive mass, in which lies the value of these 
plants for agriculture. The lateral roots of other plants, 
as of the dahlia and sweet potato, swell out at their ex- 
tremities to tubers. 
Crown Roots.—Monocotyledonous plants, or Hndogens, 
z.¢., plants whose seeds do not split with ease into two 
nearly equal parts, and whose stems increase by inside 
growth, such as the cereals, grasses, lilies, palms, etc., 
have no single tap-root, but produce crown roots, i. ¢., 
a number of roots issue at once in quick succession from 
the base of the stem. This is strikingly seen in the onion 
and hyacinth, as well as in maize, 
Rootlets.—This term we apply to the slender roots, 
usually not larger than a knitting needle, and but a few 
inches long, which are formed last in the order of growth, 
and correspond to the larger roots as twigs correspond to 
the branches of the stem. 
THE OFFices oF THE Roor are threefold: 
1, To fix the plant in the earth and maintain it, in most 
cases, in an upright position. 
2. To absorb nutriment from the soil for the growth of 
the entire plant, and, 
3. In case of many plants, especially of those whose 
terms of life extend through several or many years, to 
serve as a store-house for the future use of the plant. 
1. The Firmness with which a Plant is fixed in the 
Ground depends upon the nature of its roots. It is easy 
to lift an onion from the soil, a carrot requires much more 
force, while a dock may resist the full strength of a pow- 
erful man. A small beech or.seedling apple tree, which 
has a tap-root, withstands the force of a wind that would 
prostrate a maize-plant or a poplar,which has only side roots, 
In the nursery it is’ the custom to cut off the tap-root of 
