OrR-—LEAF GLANDS OF DIOSCOREA MACROURA. 61 
Underlying this cutinised epithelium are two or three layers 
of smaller, thin-walled cells, which form a compact sheath, 
partially enclosing the gland, and separating it from the larger, 
chlorophyll-containing cells of the mesophyll. This sheath does 
not extend beyond the upper extremity of the gland. 
The actual secretory tissue of the gland consists of a large 
number of vermiform, filamentous outgrowths, each the product 
of a single epithelial cell. ‘These are produced solely from the 
basal epithelium, from which they project into the lumen of the 
gland, there becoming intertwined to form a tangled plexus, the 
interstices of which are filled with a tenaceous fluid, possessing 
a strong affinity for such stains as corallin, Hoffman’s and 
methylene blue. In the living state of the plant, this fluid forms 
a medium, which appears to be eminently suited to the growth 
and development of the bacterium which abounds in it. 
Fic. 1,.-A portion of the secretory tissue of a mature gland. sc., vermiform secretory 
elements ; b., fluid content, with bacteria ; ep., cuticularised epithelium. x 250. 
In the mature gland, these filamentous outgrowths are sub- 
divided by cross septa into as many as six elongated cells, which 
are nearly circular in section, but, unlike the epithelial cells, 
they have thin walls, although the basal cell of each filament 
may show a certain amount of cuticularisation in its lateral walls. 
The nuclei of these cells are particularly prominent, and usually 
there are one or more large vacuoles in the cytoplasm. An 
enlargement of some of these features of the glandular tissue 
will be found in fig. 1. 
