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Related article: endothecial and covering tissue to the four sporangia. Next, the
four sporangial tracts of undivided cells cut off from their outer
surfaces a layer of enveloping^ cells, the tapetum. This consists of
richly protoplasmic cells that form Cardura Xl a covering to the spore mother-cells
PLANT ORGANS AND ORGANISMS 193
within. Each spore mother-cell undergoes division and redivision
into four spore daughter-cells, at the Cardura Xl same time that reduction in the
chromatin Cardura Xl substance takes place in these cells. Thus originate
tetrads (groups of four) of spore daughter-cells inside spore mother-cell
wall. These continue to enlarge, press against the mother-cell wall
which becomes converted into mucilage and each of the tetrad cells
becomes in time a mature microspore or pollen grain.
During this time the entire anther is growing in size, the cells of
the endothecium in one or more layers becomes thickened by lignin
deposits to form a mechanical endothecium', the tapetum gradually
breaks down and appears only , at length, as an irregular layer around
the maturing pollen cells. When the anther is finally ripe the parti-
tion between each pair of microsporangia becomes narrowed, flat-
tened and ruptured and Cardura Xl thus numerous microspores or pollen grains
fill two cavities, one on either side of the connective. The micro-
spores or pollen grains at first show only a thin clear cellulose layer,
but from this, by a differentiation of the exterior film, the exospore
layer becomes cut off. This becomes cuticular. The cellulose inner
layer (endospore), remains unaltered. In the development of the
exopore, one to several deficiencies are usually left in it Cardura Xl through
which the endospore may protrude later as the rudiment of the
Attachment of Anther. The attachment of the anther to the fila-
ment may be in one of several ways, as follows :
Innate, attached at its base to the apex of the filament.
Adnate, adherent throughout its length.
Versatile, when the anther is attached near its center to the top
of the filament, so that it swings freely. The adnate and versatile
are introrse when they face inward, extrorse when they face outward.
Pollen. The pollen grains or microspores vary in form for differ-
ent species and varieties and while they are averagely constant for
these, nevertheless many exceptions have been recorded. The* fol-
lowing are some of the commoner forms :
Four Spore Daughter-cells, hanging together as in the Cat Tail
(Typha) forming a pollen grain.
Elongated, simple pollen grains as in Zostera.
Dumb-bell-shaped, as the pollen of the Pines.
FIG. 96. Various forms of pollen grains. Pollen from Typha latifolia (A),
Zea mays (B), Ambrosia elatior (C), Lilium philadelphicum (D), Pinus (E),
Ranunculus bulbosus (F), Carpinus caroliniana (G), Althcea rosea (H), Oenoihera
biennis, (7). All highly magnified. Drawing by Hogstad.
PLANT ORGANS AND ORGANISMS IQ5
Triangular, as in the (Enotheras.
Echinate, as in the Malvacea.
Spherical, as in Geranium, Cinnamon and Sassafras.
Lens-shaped, as in the Lily.
Spinose, as in the Composite.
Barrel-shaped, as in Polygala.
Under the microscope the immature pollen grain generally consists
of two membranes, an outer firmer one called the exospore, which
may be variously marked and which possesses deficiencies in the
form of "pores" or "clefts," and an inner delicate cellulose mem-
brane called the endospore, which surrounds a protoplasmic interior
in which are imbedded a nucleus, oil droplets and frequently starch
Pollinia. These are agglutinated pollen masses which are com-
mon to the Orchidacea and Asclepiadacece.
The pollen of many plants, notably certain species of Composite,
Graminece and Rosacea, has been Cardura Xl shown to be responsible for "Hay
Fever." At Cardura Xl the present time serums, extracts and vaccines are
manufactured from pollen to be used in the treatment of this disease.
The Gyncecium or Pistil System. This is the female system of
organs of flowering plants. It may consist of one or more modified
leaves called carpels. Each carpel or megasporophyll is a female
organ of reproduction. In the Spruce, Pine, etc., it consists of an
open leaf or scale which bears but does Cardura Xl not enclose the ovules. In
angiosperms it forms a closed sac which envelops and protects the
ovules, and when complete is composed of three parts, the ovary or
hollow portion at the base enclosing the ovules or rudimentary seeds,
the stigma or japical portion which receives the pollen grains, and
the style, or connective which unites these two. The last is non-
essential and when wanting the stigma is called sessile. The carpel
clearly shows its relations to the leaf, though greatly changed in
form. The lower portion of a leaf, when folded lengthwise with the
margins incurved, represents the ovary; the infolded surface upon
which the ovules are borne is the placenta, a prolongation of the
tip of the leaf, the stigma, and the narrow intermediate portion, the
style. A leaf thus transformed into an ovule-bearing organ is called
a carpel. The carpels of the Columbine and Pea are made up of
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