n6 The Waterlilies. 



raised up at one edge or blown completely wrong side up. The toughness 

 of the lamina prevents its tearing. Breadth of leaf surface is carried to 

 its ultimate extent in the circular leaves. The larger the leaves the less 

 easily they will be overturned, and a further need will be appreciated 

 when it is noted that waterlilies must have all of their foliage in one 

 plane ; a distribution in space of three dimensions is not available to them. 

 That the rounded outline has been acquired by a backward extension of 

 the basal lobes of the leaf is due to the third condition. A round lamina 

 with marginal attachment of the petiole is quite a possible thing. But if 

 such a leaf were to exert any tension upon its anchorage, the effect would 

 be to submerge the basal portion. The central attachment obviates this 

 difficulty ; and peltation is a further advance toward the same end. 

 Various other adaptations of the plant in irritable response to its peculiar 

 environment have been referred to in previous pages. A number of 

 interesting activities of the floral parts will be described shortly. 



The nutritive relations of waterlilies have not been specially worked 

 out. They require a large amount of nitrogenous food, as every cultivator 

 can testify, but prefer it in the form of nitrates rather than ammonia. 

 Excess of calcium, as in limestone waters, is not beneficial. Doubtless 

 these substances are absorbed with water by the roots directly, since no 

 root-hairs are present. And the importance of the roots is shown by the 

 great reduction in vigor of plants when moved from one pot to another, 

 though they soon regain their strength. Wachter (1897) has shown, how- 

 ever, that complete removal of the roots is less injurious than removal of the 

 leaves. Water is also absorbed elsewhere than at the roots. A leaf of 

 N. rubra 35 cm. across, severed from the parent plant and left floating in 

 the water, with the end of the petiole tied to a stick above the water level, 

 not only remained apparently healthy for three days, but grew 1.3 cm. in 

 diameter, and its petiole elongated 6.3 cm. Whether or not this leaf was 

 transpiring moisture through the stomata I cannot say ; but that a large 

 amount of transpiration occurs from waterlily leaves was shown by a small 

 tank in my father's garden. This was a water-tight iron vessel four feet 

 square, and the surface was almost completely covered with leaves so 

 that very little free evaporation could occur. After every clear summer 

 day it was necessary to add one to three buckets of water to keep the 

 level constant. So reduced is the xylem in the petioles that one questions 

 how and where any sap can ascend. Some have thought the small 

 air-canals in the vascular bundles are filled with liquid, but we find no 

 evidence of this. But, in a leaf placed with the end of the petiole in 



