The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1894-06-10


When the cell which constitutes the
body of the plant has attained by
growth its limit of size, 1t gives rise, by
some form of cell-diyision, to one or
more new cells, which then grow. and
constitute one or more new plants.
Good examples of this are afforded in
the lowly organized unicellular algae
and fungi. Vegetative reproduction is
also found in more highly organized
plants, where parts of the body of the
plant become separated from one an
other and develop into individual
plants. This. is especially noticed in the
MOSES, and in a great number of plants
this process is effected by means of
specially modified embryonic shoots or
buds.
Although yegetative reproduction is
in many cases very effectual, yet very
many plants possess the property of
reproducing themselves by means of
spores, which are for the most part
single cells. The main point concern
ing the development of spores is that
they are produced in one of two ways,
either asexually or sexually. In the
former case they are directly produced
from the protoplaSm of a single repro
ductive organ, to which we may apply
the general term sporangium- In the
latter case the spores are not formed
from the protoplasm of single repro
ductive organs, but from the fused
protoplasm of two distinct reproduc-
tive organs. In those cases in which
the spore is capable of terminating i'm
mediateiy on the completion of its de-
velopment the cell-wail is a single deli
cate membrane consisting of celluloSe;
but in those cases in which the spore
may have to pass through a period of
quiescence or resting before germina-
ton, the wall is thick and consists of
I,x "a o1dnGnnrp
which consists of cellulose, and an
outer, the exospore, which is thick and
rigid.
Having shown the modes of reproduce
tinon of the pleridophyta (or ferns) we
will now take up the phanerogamia Tor
lone Towering plants) In the phaneno-
gamia the changes begun in the pterl-
dophyta, proceed step further: The
differentiation into male and female
organs of reproduction is carried back
far beyond the formation of the micro
spores (pollengrains) and macrospores
(embryo sacs); the macroSpore does
not sever it's connection with the par
ent plant, but continues to be nourlSh-
ed by it until after the embryo is
formed; and as a consequence of its
maintaining its structural connection
with the parent plant, the prothalIlum
is but feebly developed.
The leafy plant produces two kinds
of reproducing cells, viz: the pollen
grains and the embryo sacs. which cor
respond respectively to the microscopes
and the macrospores. The pollengralns
are for the most part single cells, which
develop from mother-cells in the in
terror of modified leaves; they soon be-
come free and are more or less SPHERE
cal in shape. The embryo sacs are
thin walled-cells which arise axially in
the ovules, structures which appear
to be homologous to the macrosporagla
of ptendaphyta Cor ferns), they do not
become free, but continue TO be IN
organic connection with the cells OF the
surrounding tissues. The portions OF
the plant-body which produce pollen
grains and embryo sacs are in general
considerably modified; thus the axis Is
generally short, the leaves delicate or
otherwise different from foliage leaves,
and containing little or no chlorophyll;
they are usually of some other color
than green. These modified parts, to
gether with the organs more lmmedl-
ately connected with the male and fe>
male reproductive cells, constitute what
is known as the flower.
The development of the flower as a
whole is an important and instructive
object of study The law Of greater
structural similarity in the earlier
of organisms becomes very evident
when we look carefully into the devel-
opment of flowers Very many flow
ers which, when fully formed, have lit
tie resemblance to each other, are
found to be exactly alike in their ear
lier stages. Without entering further
upon this subject, which is too broad
to treat in this short paper, it need
only be said here that all the floral or
CANS are essentially alike in form and
structure upon their first appearance;
the sepals, petals, stamens, and pistilS
appear at first as small popillae, and
it is only after they have grown some
what that the nature Of the nascent
organ can be determined by its shape.
Moreover it is found (es has so oftG2-
been seen in the development Of ami
mals) that the rudimentS of some or
gans which are wanting in the fully
formed flower are present in its earlier
stage.
As the flower develops. its parts be-
come more and more distinct; the
ovule becomes surrounded 10y one or
two thin cellular coats, which grow
from it's base, and almost completely
enclose it, little orifice only, the
micropyle, being left at its apex. It is
now ready for fertilization, which
takes place as follows: The pollingrain,
resting upon the moist surface of the
stigma, absorbs moisture and germi-
mates, sending out a tube which pene-
trates the soft tissue of the stigma
and style finally reaching the cavity
of the ovary, where it enters the mi
cropyle of an ovule. Here it comes in
contact with the apex of ths oyule
body, through whose ti--L~ Il forces
its way until it reaches the embryo
sac The first re5ul. of fertilizaticE is
the formation of a wall of celluiose
around the germ-cell; the latter soon
divides transverse1y one or more times,
and thus gives rise to a row of cells.
the suspensor, at the extremity of
which a rudimentary embryo is soon
formed. While the embryo is growing
the ovule increases greatly in size, and
its coat becomes hardened or other
wise modified. Internally, the endo-
sperm in the embryo sac grows still
more rapidly, and finally entirely re-
places the other tissues Of the oyule.
Thus the fully formed embryo has an
axis, the cotyledonS, a growing point
above the whorl of cotyledons, and a
rudimentary root, which IS the true
radicle.
When the ovule and its contained
embryo reaches this stage they con-
stitute the seed. The growth of the
embryo is suspended, and the tissues
which maintained organic connection
between the ovuie and the parent plant
are absorbed, thus setting the seed free.
Let us consider fertilization a little
further. The fertilization of the germ
cell involves two operations, viz: Pol
lination, i. e., the deposition of the pol
lin upon the stigma, and fertilization
proper. The latter has been spoken of
above, so it is now necessary to speak
of the former.
wanting in means of locomotion, they
are dependent for transportation to
,,.ot, ny /o,a