LESSON 5.] 



MORPHOLOGY OF ROOTS. 



31 



a tree exposes to the air, as compared with the surface of its 



twigs. 



69. The absorbing surface of roots is very much greater than 



it appears to be, on account of the root-hairs, 



or slender fibrils, which abound on the fresh and 



new parts of roots. These may be seen with 



an ordinary magnify ing-glass, or even by the 



naked eye in many cases ; as in the root of a 



seedling Maple (Fig. 55), where the surface is 



thickly clothed with them. They are not root- 

 lets of a smaller sort ; but, when more magnified, 



are seen to be mere elongations of the surface 



of the root into slender tubes, which through 



their very delicate walls imbibe moisture from 



the soil with great avidity. They are com- 

 monly much longer than those shown in Fig. 



56, which represents only the very tip of a root 



moderately magnified. Small as they are indi- 

 vidually, yet the whole amount of absorbing 



surface added to the rootlets by the countless 



numbers of these tiny tubes is very great. 



79. Roots intend- 

 ed mainly for ab- 

 sorbing branch free- 

 ly, and are slender 

 or thread-like. When the root is prin- 

 cipally of this character it is said to be 

 fibrous ; as in Indian Corn (Fig. 42), 

 and other grain, and to some extent in 

 all annual plants (41). 



71. The Root as a Storehouse of Food. 



In biennial and many perennial herbs 

 (41), the root answers an additional 

 purpose. In the course of the season it 

 becomes a storehouse of nourishment, 

 and enlarges or thickens as it receives 

 the accumulation. Such roots are said 

 to be fleshy ; and different names are applied to them according \Q 



FIG. 57 58, 59. Forms of fleshy or thickened root*. 



