320 ON THE CUTICLE OF PLANTS. 
layer with the incorporated network, and increases to a con- 
derable thickness. 
This diversity of views led me to institute a series of ob- 
servations on the subject, the result of which is exhibited in 
what follows : 
If a transverse section of epidermis be treated with iodine, 
in most cases the walls of the epidermal cells remain unco- 
loured, and only in particular instances, as in the leaf of 
Cycas revoluta, Hakea pachyphylla, Elymus arenarius, they 
assume a more or less deep yellow tinge; the coat, however, 
whether thin or thick, which covers the surface of the epi- - 
dermis, becomes under the same treatment, deep yellow or 
brown. If the epidermis thus treated with iodine be now 
placed in sulphuric acid, the portion of the cells which before 
remained colourless dissolves, and in so doing, in many cases, 
assumes a fine indigo; the yellow outer coat or cuticle, on 
the contrary, remains undissolved. This latter phenomenon 
is not however exhibited precisely in the same way by all 
plants; in most cases, the sulphuric acid has no influence, m 
other cases the cuticle is changed into a dark brown, which 
often fades after a certain time; in other cases, the cuticle 
becomes somewhat loose, without any real dissolution, while 
commonly many little air-bubbles are developed in its sub- 
stance, doubtless in consequence of the decomposition of the 
contained carbonic-acid salts. 
On examining delicate transverse sections of soft organs 
which are not coated with a leather-like epidermis; as mem- 
branous leaves, herbaceous stems, petals, stamens, ovaries, 
we find commonly the outer layer, which is coloured yellow 
byiodine, very thin. The coats of the epidermal cells are 
either all of tolerably equal thickness; e. g. Elymus are 
narius, (fig. 1), Vanilla planifolia, Helleborus fcetidus, (fg- 2); 
or the outer wall of the epidermal cells is decidedly thicker 
than the lateral and inner walls; e. g. in the leaves of 
fimbriata, (fig. 4), Dianthus plumarius, (fig. 3), and the s" 
mens of Tulipa Gesneriana, (fig. 5). - UT 
