SECTION 5.] 



ROOTS. 



33 



Section V. HOOTS. 



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

 from roots in ordinary cases, as is generally thought, but roots from Btems. 

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

 they rise from subterranean steins. 



66. 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 Fig. 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-branches for several years, unless 

 accidentally injured, as a strong tap- 

 root. But commonly the main root 

 divides off very soon, aud is lost in the 

 brandies. Multiple primary roots now 

 ami then occur, as in the seedling of 

 Pumpkin (Fig. "27), where a cluster 

 is formed even at the first, from the 

 root -end of the caulicle. 



G7. Secondary Roots are those 

 which arise from other parts of the 

 stem. Any part of the stem may 

 produce them, but they most readily come from the nodes. 



As a general 



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 supplied 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 division, 

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

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

 underground give out roots as freely as roots themselves give oil' branches. 

 Siems 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- 

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

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

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

 roots, and so become an independent plant. 



Fig. 81. Seedling Maple, ofthe natural size; therool well supplied with root-hairs. 

 here large enough to in- Been by the naked eye. 82. Lower end <>f tins root.nmgni- 



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



3 



