PLANT ORGANS AND ORGANISMS 87 
dermatogen, producing epidermis; and calyptrogen, producing the 
root cap. 
Differences Between Root and Stem 
The Root 
The Stem 
I. 
Descending axis of plant. 
1. Ascending axis of plant. 
2. 
Growing point sub-apical. 
2. Growing point apical. 
3 - 
Contains no chlorophyll. 
3. Chlorophyll sometimes present. 
4 - 
Branches arranged irregularly. 
4. Branches with mathematical regu- 
larity. 
5 - 
Does not bear leaves or leaf rudi- 
5. Bears leaves and modifications. 
ments. 
6. 
Structure comparatively simple. 
6. Structure better defined. 
Classification of Roots as to Form. — i. Primary or first root, a 
direct downward growth from the seed, which, if greatly in excess of 
the lateral roots, is called the main or tap root. Examples: Taraxa- 
cum, Radish. 
2. Secondary roots are produced by the later growths of the stem, 
such as are covered with soil and supplied with moisture. Both 
primary and secondary roots may be either fibrous or fleshy. 
The grasses are good examples of plants having fibrous roots. 
Fleshy roots may be multiple, as those of the Dahlia, or may assume 
simple forms, as follows: 
Fusiform, or spindle-shaped, like that of the radish or parsnip. 
Napiform or turnip-shaped, somewhat globular and becoming 
abruptly slender then terminating in a conical tap root, as the roots 
of the turnip. 
Conical, having the largest diameter at the base then tapering, as 
in the Maple. 
3. Anomalous roots are of irregular or unusual habits, subserving 
other purposes than the normal. 
4. Adventitious roots are such as occur in abnormal places on the 
plant. Examples: Roots developing on Bryophyllum and Begonia 
leaves when placed in moist sand. 
5. Epiphytic roots, the roots of epiphytes, common to tropical 
forests, for example, never reach the soil at all, but cling to the bark 
of trees and absorb nutriment from the air. Example: Roots of 
Vanilla. 
