MORPHOLOGY OF ANGIOSPERMS. 105 



cases produce roots from the nodes, as in Mentha spicata (Fig. 

 67). These latter are known as stolons or runners. 



Furthermore the stems of a number of plants grow under- 

 ground and these are known as rhizomes or root-stocks ; from 

 the upper portion of the nodes overground branches arise which 

 bear leaves (so that the work of assimilation may be carried on) 

 as well as flowers, and from the lower- surface, roots. A familiar 

 exam.ple of this type of plant is the May-apple {Podophyllum) 

 (Fig. 68). " 



Fig. 69. Specimens of "orris root" of commerce consisting of peeled pieces of the 

 rhizomes of Iris fiorentina. The rhizomes are mostly dichotomous, the branches becoming 

 obconical and of characteristic shape. 



While most rhizomes are perceptibly thickened, and more or 

 less fleshy when fresh, as Sanguinaria, in other instances they are 

 of the ordinary thickness of the overground stem. 



There are some rhizomes that are excessively thickened, as 

 in the common white potato, and these are called tubers. The 

 so-called " eyes " represent the nodes, from which the leaves 

 and branches arise. Tubers should not be confounded with 



