‘ 
410 Mr. Robert Brown on the Structure of the 
commonly received : but this hypothesis being soon after aban- 
doned, their statement respecting the ovulum was rejected 
along with it. 
In the ovulum of Kingia, the inner membrane, with rela- - 
tion to the external umbilicus, is inverted ; and this, as I have 
already observed, though in direct opposition to M. Turpin’s 
account, is the usual structure of the organ. There are, how- 
ever, several families in each of the two primary divisions of 
phzenogamous plants, in which the inner membrane, and con- 
sequently the nucleus, agrees in direction with the testa. In 
such cases the external umbilicus alone affords a certain indi- 
cation of the position of the future embryo. 
It is an obvious consequence of what has been already stated, 
that the radicle of the embryo can never point directly to the 
external umbilicus or hilum, though this is said to be gene- 
rally the case by the most celebrated carpologists. 
Another observation may be made, less obviously a conse- 
quence of the structure described, but equally at variance with 
many of the published accounts and figures of seeds; namely, 
that ‘the radicle is never absolutely inclosed in the albumen ; 
but, in the recent state, is either immediately in contact with 
the inner membrane of the seed, or this contact is established 
by means of a process generally very 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 deviation, but in a case altogether so pe- 
culiar, that it can hardly be considered as setting it aside. 
It is necessary to observe, that I am acquainted with excep- 
tions to the structure of the ovulum as I have here described 
it. In Composite its coats seem to be imperforated, 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 Euo- 
nymus, which, contrary to the usual structure of the genus 
* Linn. Soc. Transact. xii. p. 136. 
and 
