26 BOTANY 
to the caruncle of the castor bean, but, being much 
larger, is called an aril. © ; 
The Maize grain (Figs. 19-21) is a fruit and not a 
seed; but it differs from the fruit of the sunfiower. 
Whereas, in the latter, the seed case is merely a loose 
covering which can be removed, in the former, this 
ease has coalesced with the coat of the seed, and 
formed a single envelope which is firmly united with 
the food materials within. If on the growing corn-cob 
the development of the maize grain is carefully watched 
from day to day, it will be noted that there is no 
shedding of a seed case, and that therefore the ovary 
wall must fuse with the seed-coat and form part of the 
grain itself. Externally the grain is a blunt wedge- 
shaped body flattened on one side and having a rough 
apex which shows its point of attachment to the cob, 
and in which is the opening that corresponds with the 
micropyle of a dicotyledon. This may be located by 
placing the grain in hot water, when a bubble of air 
comes out as in the case of the castor bean. On the flat 
side, is a more or less triangular depression bisected 
vertically by a narrow ridge which indicates the 
position of the radicle and plumule. Now take a 
well-soaked grain,and, with a pin, prick away, from the 
side remote from the depression, the endosperm, which 
above and on the outside consists of amber-coloured 
matter, and further in of white easily powdered 
substance. In this way a tough elastic shield-shaped 
body will be exposed. This is the cotyledon, attached 
to the front of which may be seen the plumule and 
radicle forming a straight line on the flat side. Now 
split another grain through the flattened sides as shown 
in Fig. 21. In this, with the assistance of a lens, the 
structure of the young shoot may be seen. The iodine 
test shows that the endosperm is chiefly starch. When 
a drop of nitric acid is applied to the eut surface of 
the grain, the cotyledon becomes yellow, showing the 
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