Glands of the Plumb agineae. 251 
colour and texture. The swelling which indicates the exist- 
ence of the cavity at the base of the cotyledons of these 
genera is wanting in the Plumbago studied. Examples of 
different ages were closely examined, revealing The fact that 
no mucilage-glands exist at the base of the cotyledons. 
Mettenian glands are as usual present on the cotyledons, and 
they likewise occur sparingly on the hypocotyledonary axis. 
A seedling which had the plumule destroyed at an early 
stage continued to vegetate by its cotyledons alone, which 
persisted for many months. They were ultimately if in. 
long and f in. broad, and presented the very noteworthy 
phenomenon of bearing, like the leaves, chalk-scales on their 
under surface. 
Conclusion. 
It has been found convenient above to draw a hard and 
fast distinction between the two sets of secreting organs, viz. 
the Mettenian glands which are universally distributed over 
the vegetative organs, and the mucilage-glands which are 
confined to the axillary regions. As already hinted, however, 
glands displaying every stage of gradation from the one form 
to the other are met with in great abundance. Often, as in 
those of the axils of most species of Acantholimon and Plum- 
bago , one has difficulty in deciding which name to apply. 
They offer no feature of distinction in the very earliest stages 
of development. At all times they respond to stains and 
reagents in an exactly similar manner. 
The difference in their mucilage-secreting power is only 
one of degree. Young leaves of Statice fruticans for example, 
five or six inches long, sometimes have their whole upper 
surface bathed in mucilage, undoubtedly secreted by the 
Mettenian glands. The leaves of Statice rosea afford another 
instance of the same condition. Aegialitis , possessing modified 
in place of typical Mettenian glands, is probably in great part 
covered with the secretion. The contents of the Mettenian 
glands are evidently always of a mucilaginous character, even 
when functioning as chalk-secreting organs. 
