322 ON THE CUTICLE OF PLANTS. 
the continuation running over the lateral walls is so thin that 
it cannot be demonstrated. In other plants, on the contrary, 
as in Tulipa, the secondary coats of the lateral walls pass 
into the inmost coat of the outer wall; and beyond this a 
number of layers are found, which are deposited merely on 
the outer wall, and not on the lateral walls. This latter for- 
mation might easily induce one to believe that the epidermal 
cells consist only of the inmost layers, which surround 
their cavity, and that all the coats deposited upon their outer 
surface do not belong to the wall of the cell itself, but are 
coats secreted upon the outer surface of the epidermis. The 
observation, however, of the forms to be adduced presently, 
e. g. Hakea pachyphylla will prove the wrongness of such an 
explanation, and show that all the secondary coats are de- 
positions in the hollow of the cells. 
A. structure apparently essentially different from that hi- 
therto noticed is found in the epidermis of many thick fleshy 
or coriaceous leaves. Here we find the outer wall of the 
epidermal cells proportionally surprizingly thick as compared 
with their other walls, and on treatment with iodine, not 
merely a thin membrane seated upon the epidermis becomes 
quite yellow, but almost the whole mass of the outer epi- 
dermal wall assumes this colour, and all this thick coat 
resists the agency of sulphuric acid. The real difference 
however of the cuticle of these leaves from that of thin leaves 
consists not in its mass, but in the circumstance that instead 
of forming an homogeneous coat, it exhibits a composition 
of different parts. We see, for instance, in a thin and clean 
cross section of Aloé obliqua, (fig. 7), the lateral walls of the 
epidermal cells continuous with the cuticle and pass into a — 
membrane covering the epidermis on its outer side. .There 
can be no doubt here that the cuticle, far from being an uni- 
form membrane deposited on the outer surface of the epi- 
dermis, consists of the combined outer walls of the epidermal 
cells and a portion of the secondary membranes deposited - 
in their cavities, and that the chemieal peculiarities of the 
