WATER-LILIES 



95 



Like all floating leaves, those of Nymphaea bear cuticle, 

 stomates and palisade- cells on the upper surface only, for 

 the under surface, being turned away from the light and 

 air, takes no direct part in the work of assimilation, and 

 does not require protection from evaporation or intense 

 sunlight. 



If the leaf or flower-stalk of a Nymphaea is cut across, 

 numerous air-canals are seen to traverse it. They lead 

 into the leaf or flower, and give buoyancy, besides carrying 

 air to the submerged organs. Into the air-spaces peculiar 



FIG. 20. Yellow water-lily. Lower surface of rootstock. 



stellate hairs project, which are stiffened by a deposit 

 of calcium oxalate. Their function has not been ascer- 

 tained with certainty ; perhaps (as Stahl believes) they 

 discourage the attacks of snails and other animals which 

 feed on submerged vegetation. Of course the stalks need 

 special defences ; for if they are much damaged, the 

 entire leaf or flower will be destroyed ; the attacks of 

 caterpillars or snails which gnaw the blades of the leaves 

 are less serious. 



When the leaf-bud begins to expand, its margins are 

 folded inwards, and the future upper surface is nowhere 

 exposed. At this time the leaf is completely submerged, 

 and completely wetted. Shortly after it has gained the 

 surface and expanded into a flat oval plate, its surface 



