Pharmaceutical botany - Lighthouse Survival Blog

THE ROOT 15
The ripened seed is the product of reproductive processes, and the
starting point in the life of all Phanerogams. The living part of the
seed is the embryo, which, when developed, consists of four parts, the
caulicle, or rudimentary stem, the lower end of which is the beginning
of the root, or radicle. At the upper extremity of the stem are two
thickened bodies, closely resembling leaves, known as cotyledons, and
between these a small bud or plumule.
The function of the cotyledon is to build up nourishment for the
rudimentary plantlet until it develops true leaves of its own.
The Root
The root is that part of the plant that grows into or toward the
soil, that never develops leaves, rather rarely produces buds, and
whose growing apex is covered by a cap.
The functions of a root are absorption, storage and support. Its
hair
Fig. 12.—Cross-section of rootlet in the region of the root hairs. {From Steiens.)
principal function is the absorption of nutriment and to this end it
generally has branches or rootlets covered with root hairs which largely
increase the absorbing surface. These root hairs are of minute and
simple structure, being merely elongations of the epidermis of the root
back of the root cap into slender tubes with thin walls.
The tip of each rootlet is protected by a sheath- or scale-like cover-
ing known as the root cap, which not only protects the delicate grow-
ing point, but serves as a mechanical aid in pushing its way through
the soil. The generative tissues in the region of the root cap are:
PLEROME, producing fibrovascular tissue; periblem, producing cortex;
DERMATOGEN, producing epidermis; and calyptrogen, producing the
root cap.