THE TEGETATIVE OEGANS OF PLANTS. 265 



taching to them a ball or pot of earth. The striking out 

 of roots from the layer is in many cases facilitated by cut- 

 ting half off, twisting, or otherwise wounding the stem at 

 the point where it is buried 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 contact with 

 the soil, and emit roots from their lower joints. From 

 these again grow new stems and new roots in rapid suc- 

 cession, 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., 22, p. 372.) 



Subterranean Stems. — Of these there are three forms 

 agriculturally interesting. They are usually thought to be 

 roots, from the fact of existing below the surface of the 

 soil. This circumstance is, however, quite accidental. 

 The pods of the pea-nut ripen beneath the ground — the 

 flower-stems lengthening and penetrating the earth as 

 soon as the blossom falls ; but pea-nuts are not by any 

 means to be confounded with roots. 



Root-StOckSi — As before remarked, true roots are desti- 

 tute of buds, and, we may add, of leaves. This fact dis- 

 tinguishes them from the so-called creeping-root, which is 

 a stem that extends just below the surface of the soil, 

 emitting roofs throughout its entire length. At intervals 

 along these root-stocks, as they are appropriately named, 

 scales are formed, which represent rudiraentary leaves. 

 In the axils of the scales may be traced the buds from 

 which aerial stems proceed. Examjjles of the root-stock 

 p,re very common. Among them we may mention the 

 blood-root and pepper-root as abundant in the woods of 

 the Northern and Middle States, and the quack-grass. 



Digitized by Microsoft® 



