Orr-—L&ar GLANDS OF DIOSCOREA MACROURA. 63 
singularly infrequent in the epidermis of the acumen, and, when 
present, are confined, more or less, to the margins. 
To investigate the origin of the glands, it was found necessary 
to select very young leaves from the region just behind the 
growing-point of the shoot, for the initial stages of development 
are passed through almost before the young leaf unfolds. The 
comparatively advanced stage represented by fig. 2 was obtained 
by cutting sections of an acumen, less than 4 mm. in length, and 
only .7 mm. broad. 
The first indication of the glands is the appearance, in the 
upper epidermis, of a simple invagination, interposed between 
the two flanges which, at this stage, are very minute and close 
together. The cells which form the walls of this pit resemble 
those of the epidermis, except that the corrugations, so obvious 
on the outer surface of the latter tissue, are absent entirely from 
the superficial layer of the gland. 
In the youngest leaves, the opposing walls of Me invagination 
aré in. close approximation to one another, but, as the acumen 
increases in size, the slit widens, and the epithelial cells at the 
base of the pit increase by radial divisions to form a flattened, 
flask-shaped cavity. The cells forming the floor of the aatity 
are rich in protoplasmic contents, and become the initials of the 
vermiform, secretory elements. Each initial cell, by growth in 
a radial divert: increases in size until it proteudes into the 
lumen, when division of the protoplast takes place. The pro- 
jecting portion of the cell is then cut off by a periclinal wall, and 
becomes the first cell of the filament. This process is repeated 
in a series of intercalary cell-divisions until each filament attains 
to its full dimensions. 
A certain amount of fluid is present in the developing gland, 
even at this stage, and, in fact, it appears almost at its inception, 
for the growing apex of the stem, and the leaf primordia, are 
bathed in it, a condition which has a particular significance, 
since this fluid also harbours the bacterium found in the fully- 
developed gland. (Plate CXCVIII., fig. 1. 
About this time, nearer the base of the rapidly enlarging 
acumen, there are indications of the formation of additional 
gland-cavities by a process of subdivision; the new “‘ pockets” 
being formed directly from the pre-existing ones, not by 
invagination, but by an inverse process. This is brought about 
by active grow th in the band of tissue immediately underlying 
the long axis of each concavity, resulting in the elevation of the 
central portion of the floor to the level of the epidermis, and thus 
forming a ridge of tissue, several cells across, which bisects the 
Original pocket longitudinally, and divides the now greatly 
distended duct into two. With the growth of the acumen, these 
