VEGETATIVE ORGANS OF PLANTS. 387 



plants which usually send out no layers are nevertheless 

 artificially layered by bending their stems or branches to 

 the ground, or by attaching to them a ball or pot of 

 earth. The striking out of roots from the layer is in 

 many cases facilitated by cutting half through, twisting, 

 or otherwise wounding the stem at the point where it is 

 biiried in the soil. 



The tillering of wheat and other cereals, and of many 

 grasses, is the spreading of the plant by layers. The first 

 stems that appear from these plants ascend vertically, 

 but, subsequently, other stems issue, whose growth is, 

 for a time, nearly horizontal. They thus come in con- 

 tact with the soil, and emit roots from their lower joints. 

 From these again grow new stems and new roots in rapid 

 succession, so that a stool produced from a single kernel 

 of winter wheat, having perfect freedom of growth, has 

 been known to carry 50 or 60 grain-bearing culms. 

 (Hallet, Jour. Roy. Soc. of Eng., 33, p. 372.) 



Suckers. — When branches arise from the stem below 

 the surface of the soil, so that they are partly subter- 

 ranean and partly aerial, as in the Eose and Easpberry, 

 they are termed Suckers. These leafy shoots put out 

 roots from their buried nodes, and may be separated 

 artificially and used for propagating the plant. 



Subterranean Stems. — Of these there are three 

 forms. They are usually taken to be roots, from the 

 fact of existing below the surface of the soil.- This cir- 

 cumstance is, however, quite accidental. The pods of 

 the peanut {Arachis hypogma) ripen beneath the 

 ground — the flower-stems lengthening and penetrating 

 the earth as soon as the blossom falls ; but these stems 

 are not by any means to b3 confounded with roots. 



Root-stocks, or Rhizomes — Trne roots are desti- 

 tute of leaves. This fact easQy distinguishes them from 

 the rhizome, which is a stem that extends below the sur- 

 face of the ground. At the nodes of these root-stocks. 



