SUBTERRANEAN SHOOTS 29 



out of the soil, the remaining portion being underground. The 

 subterranean steins are distinguishable from roots (i.) by their 

 possession of leaves and buds; (ii.) by reason of their con- 

 tinuity with axes which bear foliage-leaves, or by their aris- 



Fig. 48. — Base of Potato-plant,, showing tubers. (After Baillon.) 



ing in the axils of leaves. There are four common types of 

 subterranean shoots — rhizomes, tubers, corms, and bulbs. 



A rhizome is a more or less elongated subterranean shoot 

 which frequently extends in a horizontal direction in the soil. 

 Its stem often bears scales which are membranous, and it usually 

 gives off adventitious roots. Nearly all rhizomes are sympodia, 

 as, for instance, in Grasses, in Iris, and in the Dandelion, their 



