60 



MORPHOLOGY OF STEMS. 



be called a Monomerous tuber, namely in Nelumbium luteum 

 (Fig. 108), where it consists of a single thickened internode of 



an aquatic runner, which is accordingly quite destitute of scales 

 or buds. The growth proceeding from this simple tuber is 



necessarily from a bud of 

 the node at its apex, whence 

 also a cluster of roots is 

 produced. Of a somewhat 

 similar nature are the con- 

 catenate tubers of Apios 

 tuberosa (several of which 

 io8 are strung as it were upon 



a long filiform axis), the tubers not unfrequently being mo- 

 nomerous, although the larger ones are not so. 



117. Tubercles, as they may be termed, are of a mixed or 

 ambiguous character between tubers and tuberous roots. A good 

 example of the latter is afforded by Dahlia-roots. (Fig. 68.) 

 They yield their nourishing substance to growing buds on the 

 stem above, but do not themselves normally produce even 



FIG. 106. Forming potatoes in^various stages. 107. One of the younger ones en- 

 larged. 108. Section of a small portion passing through an eye, or bud, more enlarged. 



FIG. 108a. A monomerous (i. e. one-membered) tqber of Nelumbium luteum, formed 

 of a single internode. 



