ROOTS AS TO ORIGIN 



125 



upper parts of these plants die. You know that roots of 

 some plants can directly produce new plants. 



All these facts are important, but they form no more 

 than a starting point in the study of roots. 



42. Roots as to Origin. — Roots come from the em- 

 bryo, or from other roots, or from the shoot. Those 

 which come from the embryo or branch off from other 

 roots are called primary; those which arise from the shoot 

 are called secondary. Leaves as weU as stems sometimes 

 give off roots as branches. The leaf of begonia is an ex- 

 ample. This plant may be propagated 

 by means of cuttings from the leaves. 



A . Primary Roots. — You remember 

 that the embryo comes from a single 

 cell which is produced by the union of 

 two other cells. (See page 58.) This 

 new cell by repeated divisions and by 

 growth forms the embryo. Certain cells 

 of the embryo develop into the original 

 primary root. (See Figure j8.) 



Sometimes this original primary root 

 grows straight down and becomes much 

 larger than any of its branches. Such 

 a root is called a tap-root. Dandelions, 

 radishes, turnips, carrots, and parsnips 

 have tap-roots. (See Figure jp.) Tap-roots are more 

 commonly used for storage than are other forms of roots. 



More often, however, a tap-root is not formed. The 

 primary root divides into many branches of about equal 

 size. Such roots are called fibrous. Corn has fibrous 

 roots. 



Fig. 38. — Seedling of 

 com showing the de- 

 velopment of primary 

 roots. 



