CHAP. II. 
SEED. 
247 
&c.) ; it is frequently of a different colour from the rest of the 
seed, not uncommonly being black. In plants with small 
seeds it is minute, and recognised with difficulty; but in some 
it is so large as to occupy fully a third part of the whole 
surface of the seed, as in the Horsechestnut, Sapotacese, and 
others. Seeds of this kind have been called nauca, by Gaert- 
ner. In grasses the hilum is indicated by a brownish spot 
situated on the face of the seed, and is called by Richard 
spilus. The centre of the hilum, through which the nourish- 
ing vessels pass, is called by Turpin the omphalodium. Some- 
times the testa is enlarged in the form of irregular lumps or 
protuberances about the umbilicus ; these are called strophiolcB 
or carunculcB ; and the umbilicus, round which they are situ- 
ated, is said to be strophiolate or carunculate. Mirbel has 
ascertained that in Euphorbia Lathy ris the strophiole is the 
fungous foramen of the primine ; and it is probable that such 
is often the origin of this tubercle : but at present we know 
little upon the subject. 
The foramen in the ripe seed constitutes what is called the 
micropyle : it is always opposite the radicle of the embryo ; the 
position of which is, therefore, to be determined without dis- 
section of the seed, by an inspection of the micropyle, — often 
a practical convenience. 
In some seeds, as the Asparagus, Commelina, and others 
(fig. 188.), there is a small callosity at a short distance from 
the hilum : this callosity gives way like a lid at the time of 
germination, emitting the radicle, and has been named by 
Gaertner the emhryotega. 
At the apex of the seed, in the Orange and many other 
plants, may be perceived upon the testa a small brown spot, 
formed by the union of certain vessels proceeding from the 
hilum: this spot is the chalaza (Plate VI. fig. II. b). In the 
orange it is beautifully composed of dense bundles of spiral 
vessels and spiral ducts, without woody fibre. The vessels 
which connect the chalaza with the hilum constitute a parti- 
cular line of communication, called the raphe : in most plants 
this consists of a single line passing up the face of the seed ; 
but in many Aurantiacem and Clusiaceae it ramifies upon the 
surface of the testa. 
R 4 
