Pharmaceutical botany - Lighthouse Survival Blog

54
seminated by wind currents.
^E A
Fig. 31.—Section o£ a
grain of wheat. A , Pericarps
and seed coats; B, layer of
cells in endosperm containing
aleurone grains; C, cells of the
endosperm containing starch
grains. (From Hamaker.)
PHARMACEUTICAL BOTANY
Examples of these are seen in the Milk-
weed, which has a tuft of hairs at one end of the seed called a Coma,
and in the official Strophanthus, which has a long bristle-like appendage
attached to one end of the seed and called an awn. The wart-like
appendage at the hilum or micropyle, as in Castor Oil Seed, is called
the Caruncle.
The tegmen or inner coat surrounds the
nucellus closely and is generally soft and
delicate.
A third integument, or accessory seed
covering, is occasionally present and is
called the Aril. Ex.: Euonymus (suc-
culent).
When such an integument arises at the
micropyle of the seed , as in the Nutmeg, it
is known as an arUlode.
The Nucellus or Kernel consists of
tissue containing albumen, when this sub-
stance is present, and the embryo. Albumen
is the name given the nutritive matter stored in the seed.
MODE OF FORMATION OF DIFFERENT TYPES OF ALBUMEN
If the egg cell within the embryo sac segments and grows into
the embryo and, stretching, fills up the cavity without food mate-
rial laid down around it, it happens that the nutritive material lin-
gers in the cells of the nucellus pressing around the embryo. This is
called Perispermic Albumen. Seen in the Polygonaceas.
In by far the greater number of Angiosperms, the endosperm nu-
cleus, after double fertilization, divides and redivides, giving rise to
numerous nuclei imbedded in the protoplasm of the embryo sac out-
side of the developing embryo. Gathering protoplasm about them-
selves and laying down cell walls they form the endosperm tissue
outside of the embryo. Into this tissue food is passed constituting
the^Endospermic albumen.
In the Marantaceae, Piperacese, etc., nutritive material is passed
into the nucellar cells causing them to swell up, while to one side a
small patch of endosperm tissue accommodates a moderate amount
of nourishing substance, thus resulting in the formation of abundant
perisperm and a small reduced endosperm.