STEMS 65 



of the water-lilies, from which arise the leaves with large 

 floating blades (pads). Therefore, a rhizome does not nec- 

 essarily bear only scale leaves, but may develop also leaves 

 that become aerial; and in that case they are usually 

 large. It is evident that in plants possessing rhizomes 

 the subterranean stems are perennial, while the aerial parts 

 may be annual. 



(5) Tubers. In some plants the ends of underground 

 stems become very much enlarged for food storage. These 

 enlargements are called tubers, the best-known illustration 

 being the common potato (Fig. 64). That it is a stem 

 structure is evident from the fact that it bears very much 



Flo. 64. Potato tuber showing eyes (scale leaves and axillary buds). 



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 de- 

 veloped into branches. In planting potatoes, advantage is 

 taken of the fact that any node placed in proper conditions 

 may strike root and put out a branch. Since the eyes are 

 branch buds standing at nodes, and any piece of the 

 potato containing a bud is able to produce a new plant, it is 

 customary to cut the potato into pieces, being careful that 

 each piece contains one or more eyes. Heaping up the 

 soil (hilling up) about the base of the potato plant induces 

 the formation of more of the subterranean, tuber-bearing 



