CHAP. II. 
OVULE. 
181 
the base of the nucleus; and there it expands into a sort of 
vascular disk, which is called the chalaza (Plate V. fig. 24. 
f, 25. g). As the chalaza is uniformly at the base of the 
nucleus, it will follow that, in Orthotropous and Campulitro- 
pous ovules it is confounded with the hilum ; while it is only 
distinguished in Anatropous ones, in which alone it is dis- 
tinctly to be recognised. 
It has been remarked that the raphe or vascular extension 
of the placenta always occupies the side next the ventral 
suture of the ovary ; and that when, as in Euonymus, it is 
turned towards the dorsal suture, that circumstance arises 
from an alteration in the position of the ovule subsequent to 
its being fertilised. 
It hais also been stated that the passage through the 
primine and secundine is called the foramen ; or the exos- 
tome, when speaking of that of the primine ; and the endos- 
tome, in speaking of the secundine. Upon these Mirbel 
remarks, — " These two orifices are at first very minute, but 
they gradually enlarge ; and, when they have arrived at the 
maximum of dilatation they can attain, they contract and 
close up. This maximum of dilatation is so considerable in a 
great number of species, in proportion to the size of the 
ovule, that, to give an exact idea of it, I would compare it 
not to a hole, as those express themselves who have hitherto 
spoken of the exostome and endostome, but to the mouth of 
a goblet or of a cup. It may therefore be easily understood, 
that, to perceive either the secundine or the nucleus, it is not 
necessary to have recourse to anatomy. I have often seen, 
most distinctly, the primine and secundine forming two large 
cups, one of which encompassed the other without entirely 
covering it, and the nucleus extending itself in the form of 
an elongated cone beyond the secundine, to the bottom of 
which its base was fixed." 
In practical botany the detection of the foramen is often a 
matter of great importance ; for it enables an observer to 
judge from the ovule of the direction of the radicle of the 
future embryo : it having been ascertained by many observ- 
ations that the radicle of the embryo is almost always pointed 
to the foramen. A partial exception to this law exists, how- 
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