SEED. 
91 
100. The number of cotyledons varies in different plants, 
which circumstance has given rise to the most important di- 
visions of the vegetable tribes. There are also plants in which 
this organ is wanting, and these constitute a distinct class, 
called, 
Acotyledonous plants, which have no cotyledons in their 
seeds : such plants belong to the class Cryptogamia, or flower- 
less plants ; they have no embryo nor seeds, but are repro- 
duced from spores (minute grains resembling pollen) ; ferns 
and mosses are of this class. 
Monocotyledonous plants have but one cotyledon, or lobe, in 
the seed ; as the grasses^ liliaceous plants, palms, &c. They are 
called Endogens on account of the peculiar growth of their stems. 
Dicotyledonous plants have two cotyledons ; they include 
the greatest proportion of forest-trees, leguminous^ syngenesious 
plants, &c. They are called Exogens. 
Polycotyledonous plants have more than two cotyledons, as 
the pine and hemlock : such plants are not common. 
101. The Embryo first appears as a minute speck in the midst 
of the pulp of the nucleus, near the foramen of the ovule ; it 
gradually develops and assumes an organic state ; it lies in the 
midst of the albumen, or at some of its extremities, or, when 
there is no albumen, it fills the space within the integuments, 
as in the Leguminous plants. As the embryo becomes a plant 
by the unfolding of its parts, it must contain within itself all 
the essential organs. By laying open the seeds of many plants 
the embryo becomes visible, as in the bean, orange, and apple. 
The first part formed in the embrj^o is the axis^ its two ex- 
tremities indicating the radicle and the stem ; the latter consists 
of the node, furnished with the rudiments of a pair of leaves ; 
these are the cotyledons. That part of the axis which unites 
the radicle and the cotyledon is called caulicle^ or tigelle^ from 
the point where the cotyledons are united to the axis, a hud 
is developed ; this bud contains the rudiments of the true or 
primordial leaves, and is called the jplumule^ or plumula. It 
may be seen lying between the cotyledons. When the vital 
principle is excited to action, vessels are formed and parts de- 
veloped which were before invisible. The Radicle Fig. 117. 
unfolds itself into branches or fibers, which take 
a downward direction, as if to avoid light and air, 
from their peculiar structure, or from their attrac- 
tion toward the moisture of the soil. At Fig. 117, 
appears the embryo in a germinating state ; a rep- 
resents the radicle^ 5 th.Q^lumule^ c the funicle, by 
means of which the plant is still connected to the cotyledons ; 
lUO. Division of ])lants as respects cotyledons. — 101, First appearance of the embryo — Part first 
Toinicd — Tlie node— Plume — Radicle. 
