Ipomoea paniculata. 277 
of the gland (see Fig. 5). The gland itself can be plainly seen 
with the naked eye if the petiole is cut through horizontally, 
being distinguished in a fresh leaf from the surrounding green 
tissue by its lighter colour and greater opacity. It has very 
much the form of a flask rather flattened on the side opposite 
the insertion of the duct. This flattened side is parallel with 
the vascular cylinder of the petiole, and in large glands is only 
separated by four or five rows of cells from the common starch- 
sheath of the bundles. 
The inner walls of the gland are folded into deep crypts 
lined by secretory epithelium. This is supported on a mass 
of small-celled parenchyma, from which it is cut off by a basal 
layer of cuticularized cells which appear to wall it in (Fig. 5, 
bas : ). The roof of the gland (r\ round the exit of the duct, is 
non-glandular and composed of the small-celled tissue which 
forms the papilla and walls of the duct ; the cell-walls which 
border the lumen of the gland (like their continuation, the lining 
of the duct itself) in this region are thick and cuticularized. 
The whole gland is about as long as broad, and Fig. 5, 
which represents a radial section through the gland, might 
serve equally well for one taken horizontally, except that the 
duct in this case would be rather wider. 
In examining a number of leaves I occasionally found one 
in which two glands were present on one side, the other side 
of the petiole containing but one. In these cases there were 
two distinct papillae, rather smaller than the normal single 
one on the opposite side, sunk in a common depression 
(Fig. 2), and usually the ducts were flattened in somewhat 
different directions. The glands into which the ducts led 
were wholly distinct and quite normal. 
Structure of the Secretory Epithelium. The secretory epi- 
thelium in an active mature gland (taken from a leaf whose 
blade measured 10 cm. in length) is arranged in compact 
bundles of narrow ^prismatic cells set on end, the number of 
cells in each bundle varying from ten to twenty (see Fig. 16). 
Each entire bundle is supported on a single flattened polygonal 
cell, the upper wall of which is slightly convex. 
