332 VEGETABLE PHYSIOLOGY 
being greatly reduced. In Owvirandra as the leaf becomes 
fully developed this tissue disappears, only the veins 
remaining, so that it presents the appearance of a coarse 
grating or piece of lattice-work. The epidermis of a sub- 
merged leaf is never cuticularised, and it contains no 
stomata. In many cases large lacune are formed in the 
e 
yes Nts 8 
789 #92 ff 
ce 
ey 
mk 
Fie 141.—Srction or PerioLe or WaTeER-Lity (Nymphea alba). 
a, ¢, vascular bundles; 8, d, air-channels. 
substance of the tissue, particularly when the lamina is 
somewhat stout, as in Isoétes (fig. 140). 
In plants with floating leaves the roots and stems are 
similar in character to those of the first class. The leaves, 
however, which lie upon the top of the water, are usually 
tough and thick, their undersides being sometimes deeply 
rugose. They have not the much-divided outline character- 
istic of submerged leaves, but are usually simple and some- 
times of considerable size. Those of the Victoria regia 
are often three feet in diameter, and are turned up at the 
