Sacramento daily record-union. [volume] (Sacramento [Calif.]) 1875-1891, 1882-04-08
AGRICULTURAL PAPERS.
SERIES PREPARED ESPECIALLY FOR
TIE "REGoRD-UNIoN."
Presenting instruction Contained in Lect-
ures from the Chair of Agricult-
ure, State University.
THIRTEENTH PAPEP /

SAC2tIA3 VIZ %NJ "a vi HOobA ILL., sbN AAiN0A
larry rays. che first and last belong to the
woody zystem OF plants, and the second
and tnird to the cellular system. The
pith is too well known to need description.
The medullary sheath consists of system
of spirally, ooiled ducts, encircling the
pith. These seem not to be special organs,
but simply the vascular tissue in its early
stages of development. The layer Of wood
consists of woody fiber, interpreted with
vascular tissue. It is this vascular tissue
which gives the peculiar dotted appearance
to the ends or cross. sections of some stems,
especially those of the softer. wooded trees,
and in which the vascular tissue is aceumu-
lated in the inner parts of each layer. In
other trees, such as maple, plane tree, etc,
the vascular tissues are so minute as to be
invisible, and the wood presents a close,
regular appearance. The medullar rays
are the lines radiating from the center on
the cross. section of the stem. They are
evidently for the purpose of keeping up
the communication between the pith and
bark of the plant.
THE ACTUAL GROWTH
OF an exogenous plant takes place in the
cambum layer. This is more or less
liquid layer situated between the wood
and the bark, and consists of mucilaginous
matter. This sap is made of organizable
matter, in which new cells are constantly
being formed, some of which go inward to
form new wood, while others are deposited
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always a connective tissue of thin and very
delicate cells between the wood and bark,
and in which the process of cell multipli-
cation goes on most rapidly. 1t Is by the
annually renewed growth Of the cambiam
layer that the growth of the exogenous
stems is affected. The annual increase
being depoited in cylindrical layers,
cross section of the stem shows more or
less perfectly the wood deposited in con-
centric rings between the pith and the
bark on trees growing IN climate where
there is a marked difference between the
Temperature of different seasons; and where
there is therefore growing and dormant
season these concentlic rings are most
marked, and their number gives quite &C
curately the age of the tree. The stem not
only serves to support the foliage of the
tree, Dub IL G-sO SCANS5 e$S a SbdiIhCA
through which the liquids derived from the
soil are forced by the root up into the
leaves and growing extremities of the tree
The stem also, through the medium of It's
tissues, allows the descent of the matter
which has been accumulated from the al
mosphere by the leaves.
LEAVES.
Leaves consist of membrane of cells ar
ranged on and supported by a framework
of fbers and ducts. In the earliest stages
they are intoxicated or folded together in
the buds, but with the growth of the plant
they expand and immensely increase the
lateral surface of the plant. Some plants,
notceably the cactus, seem to have no
leaves, and the stem performing the fuuc-
ton of the leaves. Johnson expresses
their relation perfectly when he says
''many of these plants above ground are
in form all stem, while in structure and
functions they are all leaf" The green
color spoken of as being characteristic of
the cellular layer OF the outer bark is also
invariably found in all vigorous and
healthy leaves This green color is due to
the presence of chlorophyll, substance
which has already been described. In
autumn, with the cessation of growth by
deciduous trees, or at the maturity Of the
plant, as in the grains, the leaves lose
their green tint and fade or altogether lose
their color the leaf stops performing its
functions and soon after drops off
Although leaves differ greatly in
form and appearance. yet their
structure is essentially the same. The
Leaf, ike the stem, is made up Of two
distinct parasitic cellular and the woody.
The cellular part consists of the membrane
and pulp OF the leaf, and the woody part
of the framework of fbers and duets. It
is this framework which gives strength to
the leaf, and which forms the medium, or
channels. through which the sap is con-
veyed and distributed to every part Of the
leaf. The subdivisions of the ribs and
veins continue to ramify among the pulp
and membranes, even after they are so
small as to be insensible TO the naked eye.
The cellular portion of the leaf is made up
of thin walled cells, containing grains OF
chloroohyIl Different parts of the leaf
are made up by different arrangements of
the cellular tissues. In leaves which
habitually expand horizontally the IN
aided eye can detect marked differ
ence between the structure of the
upper and lower surfaces of the leaves.
The upper surface, after the thin cpl
dermis which covers both sides of the leaf
is removed, is made up of several lay
ers of elongated cells, placed endwise and
perpendicular to the surface of the leaf.
These cohere eompactly together and form
a comparatively dense surface. The cells
of the lower strata are very loosely and
L. arraapaH NTH nm
merous spaces between the cells. The
cells, if elongated, are generally found ly
ing parallel to the surface of the leaf. The
more dense and compact nature of the upper
surface of the leaf accounts for the darker
shade of green than that on the lower sur
face of the leaf All of the spaces between
the cells are filed with air and commune
cate freely with one another and with the
exterior air by means of openings in the ep-
idermis. called stomata, which viii be
presently described. 1t may readily be
seen that the structure of the leaf tends
greatly to protect it from the too great heat
OF the sun, and from the too rapid loss OF
its water by evaporation.
TIE LEAVES OF PLANTS
Which grow in arid regions are even better
protected against the effects of the sun by
having numerous layers of the elongated,
densely packed cells, which were described
as forming the upper surface of the leaf
membrane. Leaves are still further pro-
tected by the peculiar construction of the
epidermis. This covering Is composed of
from one to three layers of small. thick.
sided cells, strongly cohering together SO as
to form a membrane, which may, in most
cases, be stripped off from the pulp of the
leaf. The cells of the epidermis are often
moro or less filed with matter deposited
from liquids passing through them. The
surface of the epidermis is generally COW
cred with tain coating of wax, or white
powder, which imparts the bloom to the
leaf. This bloom is evidently intended to
make the leaf capable of turning water.
The stomata or breathing pores OF
the leaf which we alluded to are openings