STRUCTURE. 



39 



to float on water and easily detached from the parent plant and from one 

 another by reason of the brittleness of the tissues of the isthmus, these 

 tubers serve to distribute the plant widely. Waterlily leaves (" lily-pads ") 

 are eaten by large herbivorous animals (deer, &c.), which vvacle about in 

 the shallow water ; these must detach numberless tubers and leave them 

 floating about, as a person does when wading among them. Doubtless 

 also wading birds, turtles, bull-frogs and many kinds of fish accomplish the 

 same end. Special mention of the structure of these tubers will be made 

 later. 



Each of the Nymphaeas except the group just mentioned possesses 

 a short, thick, erect caudex. Where this remains throughout the year 



FIG. 13. Rhizome of ff. tuberosa. Natural size. 



in a Avet and more or less vegetative condition, it dies off in the lower 

 part as it elongates above, about keeping pace in its elongation with 

 the amount of sedimentation taking place around it. Such conditions 

 habitually surround the Xanthanthae and Chamaenymphaeae, and these 

 cannot otherwise survive. Species of the Hydrocallis group often have 

 a like perennial growth, as also sometimes have the Lotos and apocarpous 

 groups in cultivation. But the habit of all of the truly tropical members 

 (Lotos, Hydrocallis, Apocarpiae) is to be dried off completely at one 

 season of the year. In this case the large mature blooming plants 

 die and rot away. N. flavo-virens alone, with some of its hybrids, is 

 able to withdraw from vigorous flowering growth into a dry, resting 

 tuber. Young plants, however, readily store away all of their nourish- 

 ment in the caudex, which then forms a tuber from the size of a pea to 

 that of a hen's egg (or much larger in N. flavo-virens]. Such resting 



