FAMILIAR SEEDS, SfRUCTURE AND GERMINATION 5 
Cotyledons do not fill the whole of the space as in the 
broad bean, but are thin and membranous. They are 
surrounded by a mass of white substance called the 
ENDOsPERM. It is the food material. In the case of 
the broad bean this food material was stored away in- 
side the cotyledons. Here the food material is separate 
from the cotyledons, forming a separate tissue called 
the endosperm. Such seeds are known as ENpDo- 
SPERMOUS or albuminous seeds. Those like the broad 
bean are known as EXENDOSPERMOUS or exalbuminous 
seeds. 
The food material in the case of castor-oil seed is not 
starch, as in the case of the broad bean, but oil. In 
germination the cotyledons do not remain below the 
ground as in the broad-bean seedling, but after having 
absorbed most of the endosperm they come above 
ground, turn green, and act as the first foliage leaves. 
Such cotyledons are called EpicEau. 
Cotyledons which remain below the ground, as those 
of the broad bean, are called HypoGrau. 
4, Maize (mealie).—The so-called maize seed (fig. 3) 
is really a fruit, as the outer covering is not the testa 
but a covering called the pericarp formed from the walls 
of theovary. The testa is very thin and is fused to this. 
There is a striking difference between this seed and the 
two we have already described. It is an endospermous 
seed, i.e. the food material lies outside the embryo 
(cotyledon, plumule and radicle), and in this respect 
resembles the castor-oil seed, although the food material 
is starch and not oil. But the embryo contains only 
one cotyledon. Plants whose seeds contain only one 
