CHAPTER X. 
SEEDS AND FRUITS. 
MORPHOLOGY. 
A seed or matured ovule belongs to one of two categories : (1.) 
exalbuminous, (2.) albuminous, t.e., without and with albumen 
respectively. 
A broad bean is a good example of the former sort. If pre- 
viously soaked in water the examination will be facilitated. A 
black mark will be seen at one end. ‘This is the scar or hilum, 
from which the stalk has been detached. As the ovule was 
bent (see p. 109) the seed must be so. The micropyle should 
therefore be close to the scar (fig. 48), and in squeezing the seed 
a drop of water will ooze out, and prove its presence. A trian- — 
gular swelling on this side! the scar marks the position of the 
radicle, which is in part (cf. p. 143) the primary root of the 
embryo. It may be taken as a very general rule that the radicle 
of the embryo is directed towards the micropyle. This is the 
case not only in exalbuminous seeds, like those of the bean, 
but also in albuminous ones (cf. figs. 30 and 53). <A skin or 
seed-coat can readily be peeled off, consisting of a thick outer and 
a thin inner layer, developed respectively from outer and inner 
integuments of the ovule. The greater part of the seed is made 
up of two thickened fleshy cotyledons or seed-leaves, which are the 
first leaves of the embryo (c/. figs. 2 and 5). Note also the white 
pointed radicle. Now separate the seed-leaves, and observe that 
the radicle is continuous with a minute curved plumule, or primary 
shoot. The space within the seed-coats is entirely occupied by 
the embryo, and all trace of the nucellus has disappeared. The 
presence of two seed-leaves characterizes dicotyledons generally. 
A dried pea, the kernels of almond and hazel-nut, apple and 
orange pips, can all be understood by comparison with bean. 
A large and typical albuminous seed is that of castor-oil, obtain- 
able from any druggist. It is oval, flattened, and mottled. At 
one end is a small knob, the caruncle, which marks the position 
of both hilum and micropyle, for the seed is an inverted one. 
> Le., left when the bean is placed so that the scar is below and to right. 
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