IOI 
and Affinities of Trap el la. 
cylinder is bounded by a well-marked endodermis (see Figs. 
53 and 54). The air-spaces of the cortex are very largely 
developed, and are formed simply by the separation from one 
another of radial plates of cells (Fig, 53). Their arrangement 
recalls that found in the stem of Myriophyllum. Several of 
the radial lamellae of cells are found collapsed, and are drawn 
simply as lines in Fig. 53. 
The arrangement of the bundles in the axial cylinder, though 
somewhat reduced, is characteristically tetrarch. Each xylem- 
group is generally reduced to a single vessel (v.). In Fig. 54, 
however, the right-hand group is more extensive, and is in 
connection with the large axial vessel. In the four groups of 
thin-walled tissue (ph.\ which alternate with the xylems, sieve- 
tubes may be found, similar to those described in the stem, 
though not so numerous. 
The arrangement of the tissues at the apex of an adventitious 
root sufficiently resembles that given in Figs. 37 and 47, for 
the embryonic root, to render further description here needless. 
The Leaves . — As has been seen, there are essentially two 
forms of leaf found, the linear-oblong submerged leaves and 
the deltoid-rotundate floating ones. In some specimens, leaves 
intermediate in form (Fig. 63 b ) are found at the point where 
the transition from one form to the other occurs. When the 
leaves are young, and before they are unfolded, their surfaces 
are densely covered with small four-celled glands. These are 
formed in greatest numbers on their undersides. After un- 
folding many drop off, leaving, however, their pedicels — 
which are small round cells, easily distinguishable from the 
other epidermal cells. In Fig. 60 a is given the surface 
view of the epidermis of the under side of a floating leaf. 
There are present four-celled glands (gif and also their 
pedicels (gl 1 ), where the gland itself has fallen off. There are 
no stomata. These are only found on the upper surface of 
the floating leaves, where they are present in great numbers 
(Fig. 60 st.). The characteristic glands are also present, and 
are often eight- instead of four-celled (Fig. 60 gl., also Fig. 61). 
I have sometimes found stomata like that in Fig. 62, especially 
