34 



ROOTS. 



[section 5. 



68. Contrast between Stem and. Root. Stems are ascending axes; 

 roots are descendiug axes. Stems grow by the successive development of 

 mteriiodes (13), one alter another, each leal-bearing 

 at its summit (or node) ; so that it is of the essen- 

 tial natr re of a stem to bear leaves. Roots bear no 

 leaves, are not distinguishable into nodes and inter- 

 nodes, but grow ou continuously from the lower 

 end. They commonly branch freely, but. not from 

 any fixed points nor in definite order. 



^.-~s„^^ 69. Although roots 



/C > / \ -/>.G^^^ generally do not give 

 ^^ . \ \M^^^^ I'ise to stems, and there- 

 fore do not pro])agate 

 the plant, exceptions are 

 not uncommon. For as 

 stems may produce ad- 

 ventitious buds, so also 

 nuiy roots. The roots of 

 the Sweet Potato among 

 herbs, and of the Osage 

 Orange among trees 

 freely produce adventi- 

 tious buds, developing 

 into leafy shoots ; and 

 so these plants are 

 propiigated by root-cut- 

 tings. But most growtiis 

 of subterranean origin 

 which pass for roots are forms of stems, the common Potato for example. 



70. Roots of ordinary kinds and uses may be roughly classed \\\\q jUjroiis 

 SiwA Jleshy. 



71. Fibrous Roots, such as those of Indian Corn (Fig. 70), of most 

 annuals, and of many perennials, serve only for absorption : tliesc; arc 

 slender or thread-like. Fine roots of this kind, and the fine branches which 

 most roots send out are called Eootlets. 



72. The whole surface of a root absorl)s moisture from the soil while fresh 

 and new ; and tlie newer roots and rootlets arc, the more freely do they im- 

 bibe. Accordingly, as long as the plant grows above ground, and expands 

 fresh foliage, from which moisture largely escapes into the air, so long it 

 continues to extend and multiply its roots in the soil beneath, renewing and 

 increasing the fresli surface for absoi-bing moistui-e, in proportion to the 

 demand from above. And wlien growth ceases above ground, and the 

 leaves die and fall, or no longer act, then the roots generally stop growing. 



FlQ. S3-85. Forms of tap-root 



