THE BOOT, OR DESCRIPTIVE AXIS. 



29 



eontinuing to advance, send down other roots, which in turn become columns similar 

 to trunlcs, until a single tree becomes a grove capable of sheltering an army of men. 



138. The Mangrove (Rhizopora), of the West Indies, sends down axial roots 

 from its branches. The seed germinates before detached, sending down its long 

 radical until it reaches the mud in which these trees grow. Thus the young plants 

 gain a firm standing before quitting their hold of the parent tree. 



139. To PAVOB THE DEVELOPMENT OP ADVENTITI0D8 ROOTS On any particular 

 part, teep that part in contact with moist soil. We often observe such roots to arise 

 naturally, in prostrate branches or stems, at these points wliieh touch the ground. 

 In slips, cuttings, &c., the same thing occurs artificially. Hence to increase the 

 roots of the potato vine, or corn, heap the earth against the stems. The madder 

 plant, which is cultivated solely for the rich coloring matter in its roots, is success- 

 fully treated in no other way. Its adventitious roots are excessively multiplied by 

 deep spading and high " hilling." 



140. To PBODUOB DWABP TREES it IS Only necessary, by any contrivance, to re- 

 tain a quantity of moist earth against the base of the selected brancli until it 

 strikes root. Afterwards it may be severed from the tree and transferred to the 

 soil. (Fig. 40, (i). 



141. Axial AND inaxial roots in agriculture. This distinction 

 must never be lost sight of. The former strike deep, anchor firmly, and 

 draw their nourishment from the lower strata of the soil. The latter 

 abide near the surface, and feed upon the upper soil. Hence let us learn 



a. Which class of crops requires deep and which shallow tillage : 



S. Which should succeed each other in the rotation of crops ; 



c. Which may be sown together in the mixture of crops. 



142. To transform: a tap-root to a fibrous. At a certain distance below the 

 collum sever the tap-root without otherwise disturbing the plant. The consequence 

 will be an increased growth of the lateral or fibrous roots nearer the surface of the 

 ground. • 



37. Old oak trunk with horizontal branoi bearing epiphytes and 

 parasites, a, A fern (Polypodium incanum). T>, Epidendrum con- 

 opseuni). ce. Long moss (Tillandsia). d, Misseltoe (Viscum). 

 6, Lichen. 



143. Epiphytes (sTrt, upon, <j)v-ov, a plant), a 

 class of plants, called also air-plants, have roots 

 ■which are merely mechanical, serving to fix such 



