FORMS OF STEMS. 



35 



stalks have withered. In this case the internodes are very short, and 

 the nodes are crowded together, so that the plant appears to be stem- 

 less. It is seen in perennial 

 plants, the leaves of which die 

 down to the ground annually. 

 A Rhizome or root-stock (fig. 90), 

 is a stem which runs along 

 the surface of the ground, be- 

 ing partially covered by the 

 soil, sending out roots from its 

 lower side, and leaf-buds from 

 its upper. It occurs in Ferns, 

 Iris, Hedychium, &c. By many 

 the term rhizome is applied to stems creeping horizontally, whether 

 they are altogether or only partially subterranean. A Pseudo-bulb is 

 an enlarged bulbous-like aerial stem, common in Orchidaceous 

 plants. It is succulent, often contains numerous spiral cells and 

 vessels, and is covered with a thick epidermis. In the Kohl-rabi, 

 a peculiar thickened turnip-like stem is met with. A Soboles is a 



t 



creeping under-ground stem, sending roots from one part and 

 leaf-buds from another, as in Couch grass, Carex arenaria, and Scir- 

 pus lacustris (fig. 91). It is often called a creeping root. A Tuber 



Fig. 90. Portion of Rhizome, r, of Convallaria Polygonatvun. a, A bud in the progress of de- 

 velopment. 6, A bud developed as a branch at the extremity of the rhizome, c c, Cicatrices or 

 scars, indicating the situation of old branches which have decayed. 



Fig. 91. Soboles, or Creeping subterranean stem, r, of Scirpus lacustris. fe,fe, Scales on the 

 stem, p a, Aerial portion of the plant. 1 1, Level of the earth. 



Fig. 92. Lower portion of a potato plant s s, Level of earth, pa, pa, Aerial portion bearing 

 leaves, t, Subterranean portion of stem or tubers. T, tuber showing eyes or leaf-buds, covered 

 by scales, 6, which are equivalent to leaves. 



