32 



MORPHOLOGY OF ROOTS. 



[lksson 5. 



their shape?. We may divide them all into two kinds ; 1st, those 

 consisting of one main root, and 2d, those without any main root. 



72. The first are merely different shapes of the tap-root ; which is 



Conical, when it thickens most at the crown, or whore it joins 

 Uie stem, and tajjers regularly downwards to a point, as in the 

 Common Beet, the Parsnip, and Carrot (Fig. 58) : 



Turnip-shaped or ■fiapiform, when greatly thickened above ; but 

 abruptly becoming slender below; as the Turnip (Fig. 57) : and, 



Spindle-shaped, or fusiform, when thickest in the midtlle and 

 tapering to both ends; as the common Radish (Fig. 59). 



73. In the second kind, where there 

 is no main root, the store of nourishing 

 matter may be distributed throughout 

 the branches or cluster of roots gener- 

 ally, or it may be accumulated in some 

 of them, as we see in the tuberous roots 

 of the Sweet Potato, the common Peony, 

 and the Dahlia (Fig. GO). 



74. All but the last of these illustra- 

 t rations are taken from biennial plants. 

 These grow with a large tuft of leaves 

 next the ground, and accumulate nour- 

 ishment all the first summer, and store 

 up all they produce beyond what is 

 wanted at the time in their great root, 



GO which lives over the winter. We know 



very well what use man and other animals make of this store of food, 

 in the form of starch, sugar, jelly, and the like. From the second 

 year's growth we may learn what use the plant itself makes of it. 

 The new shoots then feed upon it, and use it to form with great 

 rapidity branches, flower-stalks, blossoms, fruit, and seed ; and, having 

 used it up, the whole plant dies when the seeds have ripened. 



75. In the same way the nourishment contained in the separate 

 tuberous roots of the Sweet Potato and the Dahlia (Fig GO) is fed 

 upon in the spring by the buds of the stem they belong to ; and 

 as they are emptied of their contents, they likewise die and decay. 

 But meanwhile similar stores of nourishment, produced by the second 

 year's vegetation, are deposited in new roots, which live through the 



FIG. fiO. Clustered tuberoi 

 ^jeluiig to. 



tools of the Dalilia. witli tlio bottom of tlio slein tliey 



