Pharmaceutical botany - Lighthouse Survival Blog

THE PLACENTA 47
Compound Pistils are composed of carpels which have united
to form them, and therefore will have just as many cells as carpels.
When each simple ovary has its placenta, or seed-bearing line, at
the inner angle the resulting compound ovary has as many axile
or central placentae as there are carpels, but all [more or less consoli-
dated into one. The partitions are called dissepiments and form part
of the walls of the ovary. If, however, the carpels are joined by their
edges, like the petals of a gamopetalous corolla, there will be but one
cell, and the placenta will be parietal, or on the wall.
The OVULES are transformed buds, destined to become seeds in the
mature fruit. Their number varies from one to hundreds. In position,
they are erect, growing upward from the base of the ovary, as in the
Compositce; ascending turning upward from the side of the ovary or cell;
pendulous, like the last except that it turns downward; horizontal when
directed straight outward; suspended, hanging perpendicularly from the
top of the ovary.
In Gymnosperms the ovules are naked; in Angiosperms they are
enclosed in a seed vessel.
A complete angiospermous seed ovule consists of a nucellus or
body ; two coats, the outer or primine, and the inner or secundine ; and
a FUNICULUS, or stalk. Within the nucellus is found the embryo sac
containing the ovum or female reproductive cell.
The coats do not completely envelop the nucellus, but an opening
at the apex, called the poramen or micropyle admits the pollen tube.
The point where the coats are attached to each other and to the nucellus
is called the chalaza. The hilum marks the point where the funiculus
is joined to the ovule, and if attached to the ovule through a part of its
length, the adherent portion is called the raphe. The shape of the
ovule may be orthotropous, or straight; campylotropous, bent or
curved; amphitropous, partly inverted; and anatropous, inverted.
The last two forms are most common. A campylotropous ovule is one
whose body is bent so that the hilum and micropyle are approximated.
The Placenta
The placenta is the nutritive tissue connecting the ovules with the
wall of the ovary. The various types of placenta arrangement (pla-
centation) are grouped according to their relative complexity as
follows