249 
Glands of the Plumb agineae. 
base simply bisected. The extent of the secreting surface, 
which was formed of a few very delicate cells, is indicated by 
a dotted circle {c). 
The walls of the basal cells of older mucilage-glands, when 
acted on by a solution of caustic potash, retain distinction of 
contour but are flanked by broad mucilaginous boundaries 
internally (Figs. 61, 62). The same treatment causes great 
swelling of the walls of the secreting cells (Fig. 52), and when 
these are set free by rupture consequent on pressure they 
each appear as a mass of granular protoplasm, surrounded by 
an extremely translucent hyaline coat (Fig. 53). 
A seedling in which the cotyledons were abnormally fused 
(Fig. 51) bore many mucilage-glands. Another having the 
bases of the cotyledons still enclosed in the seed-coats, and the 
radicle projecting about one eighth of an inch, displayed eight 
or nine mucilage-glands. An embryo was picked from the 
seed before it showed any sign of pushing out the radicle. The 
cotyledons were still light greenish-yellow (etiolated), and were 
easily separable after boiling. No glands were yet developed. 
An example of A. plantaginea with the radicle just appear- 
ing beyond the investments of the seed (Figs. 54, 55) had no 
mucilage-glands, but a few of the Mettenian were present. 
From this it may be inferred that the latter appear as a rule 
on the cotyledons a little while before the former. In some 
cases, however, they seem to be simultaneous in appearance. 
A seedling of A. latifolia , when removed from the seed 
(Figs. 56, 57), allowed of the cotyledons being readily separ- 
ated from each other. On one of them a Mettenian gland in 
a very early stage of development was noticed (Fig. 58, g). 
It was not so large as many of the neighbouring epidermal 
cells, but distinguished from them by its refractive character 
and its cross-divisions. The outline of this gland at first is 
thus that of an ordinary epidermal cell. Very soon a circular 
form is assumed, and while still very young the inner concen- 
tric walls appear. The refractive specks (nuclei ?) are 
commonly visible in the inner cells (Fig. 59, n). Other two 
examples of the same species, slightly younger than the above, 
