The Republican. [volume] (Oakland, Md.) 1877-current, 1882-10-07
The Functions Of Leaves.

OF Inc law OF the formation OF leaves, Is
very interesting study, and some pre-
liminary remarks upon this point will be
OF interest, because one or more of the
varied functions of leaves depend to some
extent upon their form The leaves are
really a prolongation of the inner or
green soft bark, or the cambium layer of
the stem. They are exceedingly varied
in form, but their internal structure is
very simple. A leaf consists of an ep-
idermis, which may in some cases be
stripped from it, and consists of thick
walled cells. Under the outer skin are
the interior cells, which are oblong, ar
ranged endwise us regards the leaf, and
are placed in close contact. Below these
and down to the lower skin for nearly
three-fourths of the thickness of the leaf
are round cells. These inner cells are
abundantly provided with the green
coloring matter of the leaf, known as
chL0rOphyl, or the ''leaf green" in the
form of very minute grains adhering to
the walls of the cells, or to the starch
granules in the cells, or floating free in
the sap. This green matter gives the
color to the leaf. The skin is usually
coated with wax. All through this cell
matter of the leaf are found the ribs or
veins, which are really parts of the
stem, and consist of woody matter.
These veins or ribs are beautifully seen
in a skeleton leaf, which is the frame
work of the leaf freed from its cellular
tissue. The epidermis is sometimes
smooth, but is often beset with hairs and
glands composed of cells, and some of
which, as in the nettle and some other
poisonous plants, have the cells
filled with an acid liquid, while others
secrete a glutinous or adhesive sub
stance, and some, again, eXude a sweet
syrup known as honey-dew. The skin
is provided with an immense number of
minute pores or stomata, which are
really air ducts, and by these the outer
air is brought into direct contact and
communication with the cells of the leaf.
These stomata are ovalin form and have
the power, or instinct, of enlaSgng or
decreasing their openings rs the weather
may be moist or dry, by narrowing or
entirely closing their oval lips, Just as
the sides of an oval spring may be
brought close together. These stomata
are not found in water plants, the leaves
of which are submerged, and on floating
leaves exist only upon the upper surface
They vary greatly in size, some leaves
having only 800 upon square inch and
others having as many as 10000 in the
same space. They are few upon the
upper sides of the leaf, but exist in great
numbers upon the under surface OF all
green leaves.
Leaves vary considerably in form. The
seed leaves of the apple, bean, pea,
pumpkin, and other similar plants are
very unlike an ordinary leaf, and yet
they are leaves; those of the pumpkin
actually change into ordinary leaves as
soon as they have performed their special
office, which is the supply of food to the
young plant. The scales of some bulbs,
as the lily, the onion and others, are also
leaves. In other plants. as asparagus
for instance, the scales of the buds are
leaves, and in the hickory (shell-bark)
and lilac these bud scales transform into
foliage. In the bar-berry, some of the
| leaves take the form of spines; in the pea,
vetch and some other plants they appear
as tendrils by which the plant supports
itself, and in one variety of vetch the
whole leaf is tendril. In other cases
leaves appear like flowers, and are often
supposed to be flowers, as the common
pitcher plant of the swamps and the
Gala, generally supposed to be lily. In
the Dion9a, or Venus fiy-trap, each leaf
| is provided at the end with pair of
fleshy spined appendages, which close
when irritated by fly or foreign sub
stance. In the true East India pitcher
plant (Nepenthes) the leaf is curiOusly
| TO
spirally as watch-spring, and then en-
larges into the form of pitcher or deep
cup. at the mouth of which is lid pro-
vided with a hinge, by which it opens,
and the whole of this is only one leaf.
Other leaves are thick, fleshy, and sue
culent, as in the aloe, the house-leek, and
the EGGPLANT.
Again leaves appear to vary their form
so as to present very large surface to
the atmosphere, and to admit its passage
among them with the utmost facility they
are feathered, cleft, divided and cut with
great diversity. A moderate-sized tree
may bear several million of leaves, alto
| gether having a surface of from 100, 900
to 100000 square feet, or, if spread out,
might cover surface of four or five
acres in extent, The enormous number
of breathing pores thus continually tran
spring air or the various gases which
are mixed with it are quite beyond our
comprehension.
The function of the leaves is analogous
to the process of digestion in animals.
The water absorbed from the soil, hay
ing in solution large number of sub
stances derived from the soil, enters at
the roots, passes through the stem and
reaches the leaves, through which it cir
culates among the cells. Here it is
brought into contact with the air, in
spired by the myriads of stomata or
breathing pores in the leaves. The sap,
which consists of very weak solution
of mineral matters, is changed in its
character by the action of the atmosphere
upon it and becomes no longer sap. Its
water is evaporated by the leaves, and
the mineral and heterogeneous and CONVEX
sion into organized tissue. Sap does
not flow downward from the leaves.
There is downward current of organ
lied tissue forming substances, but not
sap, which passes along the ducts of the
cambium layer, which lies between the
bark and the wood, and from which new
bark and new wood are formed, and
| which is, in fact, a continuation of the