The Sedalia weekly bazoo. [volume] (Sedalia, Mo.) 187?-1904, 1891-03-24
LEAKAGE OF PLANTS.

Contrivances For Protection With Which
Nature Has Supplied Leaves.
All trees and plants that spring from
two-lobed seeds, that is, from seeds that
can be split like peas or acorns, have
their leaves veiEed irregularly. They
can not be torn across except by a
broken line. On the contrary, the leaves
of such plants as spring from kernel
that will not split-a grain of corn, for
example-can be slit lengthwise into
tapering strips In this way we can dis
tinguish plants that grow from seeds
that have two cOtyledons from those
whose seeds have but single cotyledon.
The leaves of discotyledonous plants,
as they are called, are of great
variety of size, shape, texture and
finish. They are not simple mem
brane, but are made up of many layers
of cells The interior OF the leaf COM
municateS with the external air by mil
lions of little mouths These are
mostly on the under surface of the leaf
This is to protect them from the sun
and secure uniform evaporation.
The surface Of the leaf is IN some
cases protected by coat of varnish
The upper side of an oak or birch leaf
will show this finish plainly. In other
cases the same object is gained by an
Increased thickening of the sap In
Australia, it is said the leaves of some
trees have vertical position, so as to
present a smaller surface TO the sun
Fleshy leaves are protected by their
thickness.
Another mode of protection is by the
growth of woody hairs. Plants of the
desert are frequently covered with felt
of hair The cactus often grows in this
way. Some spc es OF plants which are
smooth in the North become woody in
the South.
The uses of hairs are various. They
serve to check too rapid evaporation.
They protect the breath ne holes, and
as these are on the under side of the
leaf, it is the under side that is hairy.
This fact is strikingly noticeable in the
case OF the white poplar, for as the
ieaves OF this tree are in almost oon-
slant motion, the turning from one side
to the other produces a shimmering eff
feet
throw off water, and prevent the breath
ing-hoies from becoming c'ogged as
they would otherwise be with fog or
dew. This is important in some mount
ain and marsh plants. Nature resorts
to the same continuance for protection
against too much mo sture that she
uses against too little.
The hairs also serve to shade the leaf
from excessive light and heat More
than this, they protect the leaf against
insects, which would otherwise feed
upon 1T. The singing hairs on the |
common nettle save the plant from be- |
ing fed upon by the larger animals A |
coarse woody hair is equally distaste- |
full The leaf OF the holly is protected
by spines along its edges
Most leaves are glad of as much sun
shine as they can secure, and are ar |
ranged with reference TO this end. II |
we cut OFF beech twig below the sixth |
leaf, we find that the leaf area which it |
carries is about eighteen square inches |
The width of the leaf is one and three !
fourth inches This IS determined by |
the distance between the buds. If the |
leaves were broader, they would over
lap; if they were narrower, there would
be waste of space.
The area on the other hand. and the /
width on the other. being thus deter
minea, the length is fixed, because, to
secure an area of eighteen inches with |
six leaves which are about one and |
inches in width, the |
length must be about two inches -
Youths Companion.