34 



ROOTS. 



[SECTION 5. 



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

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

 iuternodes (13), one after another, each leaf-bearing 

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

 tial nature of a stem to bear leaves. Roots bear no 

 leaves, are not distinguishable into nodes and inter- 

 nodes, but grow on continuously from the lower 

 end. They commonly branch freely, but not from 

 any fixed points nor in definite order. 



69. Although roots 

 generally do not give 

 rise to stems, and there- 

 fore do not propagate 

 the plant, exceptions are 

 not uncommon. For as 

 stems may produce ad- 

 ventitious buds, so also 

 may 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 

 propagated by root-cut- 

 tings. But most growths 

 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 into fibrous 

 wsAfiesly. 



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

 annuals, and of many perennials, serve only for absorption : these are 

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

 most roots send out are called Rootlets. 



72. The whole surface of a root absorbs moisture from the soil while fresh 

 and new ; and the newer roots and rootlets are, 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 fresh surface for absorbing moisture, in proportion to the 

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

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



Fiq. 83-85. Forms of tap-root. 



