342 THE EMBRYO AND ITS PARTS. 
of the embryo-sac. The embryo being the rudimentary plant, 
it is necessarily the most important part of the seed, and it con- 
tains within itself, in an undeveloped state, all the essential 
parts of which a plant is ultimately composed. Thus we dis- 
tinguish, as already noticed in the first chapter, three parts in 
the embryo ; namely, a radicle, plumule or gemmule, and one or 
more cotyledons. These parts may be readily recognised in 
many seeds; thus in the embryo of the Lime (fig. 764), the 
lower portion, 7, is the radicle or portion from which the root is 
developed ; the two expanded lobed bodies above, c, c, are the 
cotyledons; and between these the plumule or gemmule is 
placed. In the Pea, again (fig. 16), the two fleshy lobes, ¢, ¢, 
are the cotyledons, between which there is situated a little axis, 
t (tigellum), the upper part or bud-like portion of which is the 
plumule, n, and the lower part, 7, the radicle. 
Fia. 765. These parts are still better observed when the 
embryo has begun to develop in the process 
of germination ; thus in fig. 18, which repre- 
sents the French Bean in that condition, ¢ is 
the radicle from which the roots are being 
given off below, the cotyledons are marked 
ce, c, and the plumule is seen coming off from 
between the cotyledons, and forming a direct 
continuation of the axis from which the root 
is developed below. The tigellwm or hypoco- 
tyledonary axis is generally a mere point, but 
at other times it forms a short stalk (figs. 16, 
and 748, t). Plants which thus possess two 
cotyledons in their embryo are called Dicoty- 
ledonous. But there are plants in which, as 
already neticed, there is commonly but one 
cotyledon present (figs. 705, c, and 765, c), 
and which are, accordingly, termed Monocoty- 
ledonous. In rare instances, however, a mo- 
nocotyledonous embryo has more than one 
Fig. 765, Germina- cotyledon, and then the second cotyledon 
GaE a pets alternates with the first, instead of being 
coming through opposite to it, as is invariably the case with 
hae ae Yo ts the two cotyledons of Dicotyledonous plants. 
stem, By the difference thus presented in the em- 
bryos of Flowering Plants, as already described 
in the first chapter, these plants are divided into two great 
classes, called respectively Dicotyledones and Monocotyledones. 
(a) The Monocotyledonous Embryo.—The parts of the mono- 
cotyledonous embryo are in general by no means so apparent 
as those of the dicotyledonous. Thus the embryo at first sight, 
externally, usually appears to be a solid undivided body of a 
cylindrical or somewhat club-shaped form, as in Triglochin (fig. 
767) ; but if this be more carefully examined, a litile slit, f, or 
