SECTION 5.] 



ROOTS. 



33 



Section V. ROOTS. 



65. It is a property of stems to produce roots. Stems do not spring 

 from roots in ordinary cases, as is generally tliought, but roots from stems. 

 Wheu perennial herbs arise from the ground, as they do at spring-time, 

 they vise from subterranean stems. 



60. The Primary Root is a downward growth from the root-end of 

 the caulicle, that is, of the initial stem of the embryo (Fig. 5-7, 81). If 

 it goes on to grow it makes a main or tap-root, as in Eig. 37, etc. Some 

 plants keep this main root throughout 

 their whole life, and send off only 

 small side branches ; as in the Carrot 

 and Radish : and in various trees, like 

 the Oak, it takes the lead of the 

 side-branclies for several years, unless 

 accidentally injured, as a strong tap- 

 root. But commonly the main root 

 divides oif very soon, and is lost in the 

 branches. Multiple primary roots now 

 and then occur, as in the seedling of 

 Pumpkin (Fig. 27), where a cluster 

 is formed even at the first, from tlie 

 root-end of the caulicle. 



67. Secondary Roots are those 

 which arise from other parts of tlie 

 stem. Any part of the stem may 

 produce tliem, but they most readily come from the nodes, 

 rule they naturally spring, or may be made to spring, from almost any 

 young stem, when placed in favorable circumstances, — that is, when 

 placed in the soil, or otherwise sup|)lied with moisture and screened from 

 the light. For the special tendency of the root is to avoid the light, seek 

 moisture, and therefore to bury itself in the soil. Propagation by dicision, 

 which is so common and so very important in cultivation, depends upon 

 the proclivity of stems to strike root. Stems or branches which remain 

 underground give out roots as freely as roots themselves give off branches. 

 Stems which creep on the ground most commonly root at the joints; so 

 will most branches when bent to the ground, as in propagation by layer- 

 iiuf ; and propagation by cuttings equally depends upon the tendency of the 

 cut end of a shoot to produce roots. Thus, a piece of a plant which has 

 stem and leaves, either developed or in the bud, may be made to produce 

 roots,, and so become an independent plant. 



Fig. 81. Seedling Maple, of the natural size ; the root well supplied with root-hajjs. 

 here large enough to be seen by the naked eye. 82. Lower eml of this root,niaglu- 

 tied, the root seen just as root-hairs are beginning to form a little behind the tip. 



3 



As a general 



