360 Mr. Robert Brown on the Structure of the 
plays great erudition in every branch of his subject, can hardly, 
however, be considered an original observer in this part. He 
describes the unimpregnated Ovulum as a pulpy homogeneous 
globule, whose epidermis, then scarcely distinguishable, sepa- 
rates in a more advanced stage, and becomes the testa of the 
seed, the inner membrane of which is entirely the product of 
fecundation*. He asserts also that the Embryo constantly 
appears at that point of the ovulum where the ultimate branches 
of the umbilical vessels perforate the inner membrane; and 
therefore mistakes the apex for the base of the nucleus. 
In 1806, Mons. Turpin} published a memoir on the organ, 
by which the fecundating fluid is introduced into the vegetable 
ovulum. The substance of this memoir is, that in all Phzeno- 
gamous plants fecundation takes place through a cord or fas- 
ciculus of vessels entering the outer coat of the ovulum, at a 
point distinct from, but at the period of impregnation. closely 
approximated to, the umbilicus, and to the cicatrix of this cord, 
which itself is soon obliterated, he gives the name of Micro- 
pyle: that the ovulum has two coats, each having its proper 
umbilicus, or, as he terms it, omphalode; that these coats in 
general correspond in direction; that more rarely the inner 
membrane is, with relation to the outer, inverted; and that 
towards the origin of the inner membrane the radicle of the 
embryo uniformly points. 
It is singular that a botanist, so ingenious and experienced 
as M. Turpin, should, on this subject, instead of appealing in 
every case to the unimpregnated ovulum, have apparently con- 
tented himself with an examination of the ripe seed. Hence, 
however, he bas formed an erroneous opinion of the nature 
and origin, and in some plants of the situation, of the micro- 
pyle itself, and hence also he has in all cases mistaken the 
apex for the base of the nucleus. 
A minute examination of the early state of the ovulum does 
not seem to have entered into the plan of the Jate celebrated 
M. Richard, when in 1808 he published his valuable and ori- 
ginal Analyse du Fruit. The ovulum has, according to him, 
but one-covering, which in the ripe seed he calls episperm. 
He considers the centre of the hilum as the base, and the cha- 
laza, where it exists, as the natural apex of the seed. 
M. Mirbel, in 1815, though admitting the existence of the 
foramen or mycropyle of the testat, describes the ovulum as 
receiving by the hilum both nourishing and fecundating ves- 
* Gert. de Fruct. et Sem. i. p. 57, 59, et 61. 
+ Annal. du Mus. d Hist. Nat. vii. p. 199. 
t Elém. de Physiol. Vég, et de Bot. tom. i, p. 49. 
sels, 
