138 DEVELOPMENT OF THE OVULUM 
7. Determination of the number of coats, the distinction 
of testa by raphe, and of nucleary or third coat by 
imperforate and often sphacelated apex. 
8. The explanation of the true structure of true Nym- 
pheacee, Piperacez, and Saururea, etc. 
The only point on which I would presume to differ, relates 
to the Amnios, which Mr. Brown mentions as existing in a 
few plants, although in the next paragraph it would appear, 
that he considered its existence at an early stage to be uni- 
versal, and that its non-existence is due to obliteration. 
[Apparent inversion of embryo in Lemna. 
Anomalies of testa. 
I have still to notice the modus operandi of the formation 
of the embryo. Before doing this, (which will merely.con- 
sist in a recapitulation of doctrines, all of a somewhat 
fanciful description,) it may not be amiss to sketch the usual 
mode of fecundation. 
The first steps of this all-important phenomenon, consist 
in the application of the pollen to the surface of the stigma, 
or when this organ does not exist, as in Cycadez, Conifere, 
and Gnetacea, to the ovula themselves. 
The result of this application is the invariable emission 
of the pollen boyaux, which passing through the lax tissue 
of the stigma, enter the stigmatic canal, by which they are 
guided to the placenta, and hence to the ovula; into the 
foramen of which they invariably enter. Their subsequent 
functions are as yet unknown ; but froin certain instances, it 
is lawful to conclude that they penetrate into the substance 
of the nucleus, to a greater or less depth. 
The consequence of this application, is in some cases the 
appearance of the embryonary sac, and then of the embryo; 
and in others in which the sac exists before fecundation, 
the appearance of the embryo alone. 
The actual origin of this body is, as might be expect- 
ed, involved in absolute obscurity. 
