ON THE CUTICLE OF PLANTS. 327 
coloured yellow by iodine, and the inner thick secondary 
membrane, in general not capable of being so coloured, is 
filled with fluid, through which the pollen tube, after it has 
burst through the outer membrane, descends. 
Notwithstanding the perfect proof afforded by the above- 
mentioned facts, that the cuticle is formed of the outer coats 
of the epidermal cells, this inference for a long time ap- 
peared to me very doubtful, in consequence of the raised 
lines which are found on the cuticle of many plants passing 
frequently without any interruption from one cell to another, 
(compare the cuticle of the stem of Rumex Patientia with 
that of the leaf of Helleborus fcetidus). This phenomenon, 
independent of the structure of the individual epidermal cells 
appeared to shew that the cuticle ought to be considered as 
a distinct membrane. The alleged observations, however, 
contradicted this so strongly, that I was compelled to con- 
sider it erroneous ; and in point of fact, it appears that the 
continuation of the raised lines over the commissures of the 
cells on a closer inspection does not contradict the explana- 
tion given above of the origin of the cuticle. v 
The examination of the epidermis in different periods of 
growth, shews that the epidermal cells of organs in an early 
stage of growth are perfectly smooth, and that not till after 
the deposition of secondary coats in the cells, and after the 
change of their upper surface into a characteristic cuticle, 
those elevations in the form of continuous lines or isolated 
Sranules are at all visible. Its production is a consequence 
of a partial growth in the outer layers of the epidermis, 
Which takes place at a late period of its evolution. This 
growth, and the elevation of the outer surface into stripes, 
and papille seems to stand in intimate connexion with the 
chemical metamorphosis which the cellular membrane un- 
dergoes in the course of its change into cuticle; at least, this 
View seems strengthened by the circumstance, that in many 
Species of aloés, e. g. Aloë margaritifera, the inner side of 
the cuticle is raised into warts similar with those on the 
Cuter surface; while the innermost coat, which dissolves in 
