STEMS 249 



and any nodes that remain are able to send up fresh crops 

 of aerial branches. In many cases only a single aerial branch 

 is sent up each year, as in wild ginger, Solomon's seal (Fig. 

 216), iris, bloodroot, etc. ; in others, leaves and flowers 

 may be sent up separately by the rootstock. In the common 

 ferns, the so-called fronds are simply large leaves developed 

 directly by the rootstock (Fig. 214). Perhaps even more 

 familiar is the extensive rootstock system of the water- 

 lilies, from which arise the leaves with large floating blades 

 (pads). It is evident that a rootstock does not necessarily 

 bear only scale leaves, but it may develop also leaves that 



FIG. 217. Potato tuber, showing "eyes" (scale leaves with their axillary buds). 



become aerial, and in that case they are usually large. In 

 plants possessing rootstocks, the subterranean stems are 

 perennial, while the aerial parts may be annual. 



(2) Tuber. In some plants the ends of underground 

 stems or branches become very much enlarged in connection 

 with food storage. These enlargements are called tubers, 

 the best-known illustration being the common potato (Fig. 

 217). That it is a stem structure is evident from the fact 

 that it bears very much reduced leaves, in the axils of which 

 are buds, the so-called " eyes." Abnormally developed 

 potatoes often show the shoot character of the tuber very 

 plainly, and in the case of potatoes sprouting it is evident 

 that the eyes have developed into branches. In planting 

 potatoes, as has been said, advantage is taken of the fact 



