Botany.] 
NATURAL llfSTORY. 
549 
short, but sometimes of great length, and which indeed 
in all cases may be regarded as an elongation of its own 
substance. From this rule I have found one apparent de- 
viation, but in a case altogether so peculiar, that it can 
hardly be considered as setting it aside. 
It is necessary to observe, that I am acquainted with ex- 
ceptions to the structure of the ovulum as I have here 
described it. In Composite its coats seem to be imper- 
forated, and hardly separable, either from each other or 
from the nucleus. In this family, therefore, the direction of 
the embryo can only be judged of from the vessels of the 
testa *. And in Lemna I have found an apparent inversion 
of the embryo with relation to the apex of the nucleus. In 
this genus, however, such other peculiarities of structure 
and economy exist, that, paradoxical as the assertion may 
seem, I consider the exception rather as confirming than 
lessening the importance of the character. 
It may perhaps be unnecessary to remark, that the raphe, 
or vascular cord of the outer coat, almost universally belongs 
to that side of the ovulum which is next the placenta. But it 
is at least deserving of notice, that the very few apparent ex- 
ceptions to this rule evidently tend to confirm it. The most 
remarkable of these exceptions occur in those species of 
Euonymus, which, contrary to the usual structure of the 
genus and family they belong to, have pendulous ovula; 
and, as I have long since noticed, in the perfect ovula only 
of Abelia t. In these, and in the other cases in which the 
raphe is on the outer side, or that most remote from the 
placenta, the ovula are in reality resupinate ; an economy 
apparently essential to their developement. 
The distinct origins and different directions of the nou 
Linn, Soc. Transact, xii. p. 136. i’ Abel’s Chinas p. 377 
