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 magnifying-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. 



70. 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 to 



FIG. 57, 58, 59. Forms of fleshy or thickened roots. 



