12 
THE FLORIST’S JOURNAL. 
parts above and beneath them. These functions and purposes 
of leaves are variously exemplified : thus, if a number of rings 
of bark are divided from each other by spaces without bark, 
those rings which have leaves on them will live longer than 
those which have none ; if the leaves are stripped from a plant 
whilst its fruit is immature, the fruit will not ripen, but fall off; 
if a branch is denuded of its leaves, for a whole season, it either 
dies, or does not perceptibly increase in size : thus, again, if 
the cotyledons, or seed-leaves, are destroyed, the young plant 
will increase but slowly, if at all. 
Leaves are most admirably adapted for the performance of 
their functions ; they consist, as we have seen, of a thin plate 
of cellular tissue, pierced by air vessels and woody tissue ; and 
this is enveloped by a hollow empty stratum of cells, forming 
the cuticle. Beneath the cuticle, on the upper side of the 
leaves, the bladders of cellular tissue are compactly arranged, 
perpendicular to the plane of the cuticle; whilst beneath the 
cuticle, on the lower side, they are loosely arranged : in the 
former case, they have but a small number of air cavities ; in 
the latter these abound, and are in connection with the 
stomates. To prevent too rapid an evaporation is the ordinary 
office of the cuticle ; whilst in cases where it is necessary to 
furnish the means of freely parting with superfluous moisture, 
it is provided for in the stomates, which act like valves, and 
open to permit its passage : they also seem to supply fluid, by 
opening to imbibe the moisture of the atmosphere. In leaves 
which are submersed, and where these variations, arising from 
atmospheric influence, cannot occur, neither cuticle nor sto¬ 
mates are present. 
The property of giving out and imbibing fluids, which is 
possessed by the leaves, differs considerably with respect to 
quantity, in different plants : thus, some perspire considerably 
more than their own weight of aqueous matter, in the course 
of one day; whilst others, such as succulents, perspire very 
sparingly; and the same may be said with reference to the 
quantity of fluid imbibed. These variations result from the 
presence, or absence, and the relative sizes of the stomates,- 
which exist in the outer covering of the leaf. 
Hairs are believed to aid these functions of the leaves, by 
collecting humidity from the atmosphere ; but whether leaves 
