SECTION 5.] 



ROOTS. 



35 



and their soft and tender tips harden. Prom this period, therefore, until 

 growth begins anew the next spring, is the best time for transplanting ; 

 especially for trees and shrubs. 



73. The absorbing surface of young roots is much increased by the for- 

 mation, near their tips, of Root-haies (Fig. 81, 82), which are delicate 



tubular outgrowths from the surface, through the delicate walls of which 

 moisture is promptly imbibed. 



74. Fleshy Boots are those in which the root becomes a storehouse of 

 nourishment. Typical roots of this kind are those of such biennials as the 

 turnip and carrot ; in which the food created in the first season's vege- 

 tation is accumulafed, to be expended the next season in a vigorous growtli 

 and a rapid development of flowers, fruit, and seed. By the time the seed 

 is matured the exhausted root dies, and with it the whole plant. 



75. Pleshy roots may be single or multiple. The single root of the 

 commoner- biennials is the primary root, or tap-root, which begins to 

 tliickeu in the seedling. Names are given to its shapes, such as 



Conical, when it thickens most at the crown, or wliere it joins the stem, 

 and tapers regularly downwards to a point, as in the Parsnip and Carrot 

 (Fig. 84) ; 



Turnip-shaped <yc napiform, when greatly thickened above, but abruptly 

 bcconimg slender below; as the Turnip (Fig. 83) ; and 



FiQ. 86. Sweet-Potato plant forming thickened roots. Some in the middle are 

 just beginning to thicken; one at the left has grown more; one at the right is still 

 larger. 



Fia. 87. Pasoioled fusiform roots of a Dahlia : a, a, buds on base of stem. 



