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



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

 of a single internode. 



