= 
ke 
Vase 
2%, 
i 
i 
: Sik an ees 2b ad 2 Piystabeg ical B clang. 
Oro the inner layer thin and white. The testa . Re. 
heyy. crustaceous, or even stony [as in the Brazil- nut |; 
and is either smooth (Fig. 331), or with pit-like depressions ae 
(Fig. 332), or covered with spines (Fig. 333),and may be 
white or coloured. gee 
The nucleus of the seed consists essentially of an embryo, 
in addition to which is found in the majority of seeds an — 
albumen or endosperm (Fig. 333). Seeds are therefore dis- 
tinguished into albuminous and exalbuminous. The embryo 
in its simplest 
Fic. 334. — Globular 
embryo of Pyrola, 
with reticulated 
testa (magnified). 
form (Fig. 334), as in orchids, Ovobanche, 
Monotropa, and Cuscuta, isa spherical body ; 
but as a rule consists of an axis (Figs. 97-99, 
pp. 70, 71) and one or more leaves. The axis 
is differentiated at its apex into a plumule, 
distinct from the lower end or radicle. The — 
leaves of the embryo are in most plants 
very characteristic, and different in form 
from the foliage-leaves which are subse- 
quently developed, and bear the name of 
seed-leaves or cotyledons. They are some- 
times thin and leaf-like, sometimes thick. 
and fleshy. The green colour which many — 
cotyledons assume as soon as they mise 
above the ground after germination is only 
developed under the influence of light; it is not found 
while they are still enclosed in the testa. The thicker and 
more fleshy cotyledons which often occupy the greater part 
of the seed, as in Leguminosee, have scarcely anything in 
common with the later foliage-leaves of the plant, and - 
generally remain underground after germination. Dependent 
on the number of cotyledons, plants are divided primarily 
into Dzcotyledones with two, Monocotyledones with only 
one, and Acotyledones |flowerless plants], without any. A 
larger number of cotyledons than two is rare,andis peculiar 
to certain Conifere (Fig. 335). In a féw cases, asia 
