Ipomoea paniculata. 281 
tangential and radial divisions, especially in the region of the 
internal orifice. This results in a thick cuticular rim or cushion 
of tissue, which projects into the lumen of the gland (r). The 
tissue so formed by the proliferation of the epidermis can 
easily be distinguished from the underlying parenchymatous 
ground-tissue by the layer of thickened membrane which 
separates them, and is continuous at the mouth of the duct 
with that dividing the epidermis of the leaf-surface from the 
sub-epidermal tissue. 
The inner wall of the glandular dilatation is no longer 
concave ; the floor is raised into a rounded projection in the 
centre in consequence of the multiplication of the cells 
beneath ; and the surrounding concavity is filled up from 
above by the projecting cushion of tissue (r) derived from the 
epidermis at the insertion of the duct. The epidermal cells 
lining the gland have also increased by radial divisions, so 
that the lumen, although flattened, is now wider than before 
and measures about J mm. from side to side. 
The gland has now attained its characteristic form, and in 
successively older leaves, whose blades measure i-i, 1*5, 3-8, 
6*o, and 8-o cms. respectively, the main changes consist, 
(1) in the formation of numerous folds and pits in the walls of 
the gland, caused by the repeated radial divisions of the 
lining (secretory) epithelium and the unequal proliferation of 
the small-celled parenchyma below ; (2) in the increased 
thickening of the tissue derived from the epidermal lining of 
the duct, giving rise to the roof of the gland, on the one hand, 
at the inner extremity, and on the other hand to the projecting 
papilla at whose apex the duct opens on the surface of the 
leaf ; and (3) changes in the nature of the secretory epithelium 
itself, which will be described below. Fig. 5 represents a ver- 
tical section through a fairly advanced gland, whose walls, 
however, have not yet become very much folded. The lamina 
of the leaf from which this section was taken measured 8 cm., 
and the gland itself measured £ mm. from side to side, and 
f mm. deep, including the duct. 
In the development of the gland of Ipomoea we have again a 
