56 



DESCRIPTIVE BOTANY. 



ample of the kind, equally interesting to the botanist, 

 though not treated with a like consideration by the agri- 

 culturist 



(64.) Tubers. Some subterranean stems or branches 

 terminate in swollen nodosities, analogous to those which 

 we have described as formed on the roots of some 

 plants (art. 40.). The common potato (fig. 48.) is a 



familiar example of this kind. These are called " tubers," 

 and form magazines of nutriment which serve for the 

 development of the buds or " eyes," seated upon their 

 surface. In general, the distortions produced by the 

 formation of the tuber, destroy the symmetry which the 

 buds on the surf ace of this portion of the stem would other- 

 wise exhibit, in their mode of arrangement ; but still they 

 may, in many cases, be observed to follow a spiral 

 course, characteristic, as we shall hereafter see, of the dis- 

 position of the leaves. In one peculiar variety of this 

 tuber, termed the " pine-apple potato," this disposition 

 of the buds is very striking ; each is subtended by a 

 swollen projection which represents the base of the 

 leaf-stalk, in whose axil we may consider it to have 

 been formed. In turnips, radishes, &c., this tuberous 

 development originates in the lowest portions of their 

 stems, which are placed either wholly or partially 

 below ground ; whilst in the Kohl-rabbi (a variety of 



