M. Mirbel, in 1815, though admitting the existence of the foramen or micropyle of the testa,* describes the ovulum as receiving by the hilum both nourishing and fecundating vessels,** and as consisting of a uniform parenchyma, in which the embryo appears at first a minute point, gradually converting more or less of the surrounding tissue into its own substance; the coats and albumen of the seed being formed of that portion which remains.***
(*Footnote. Elem. de Physiol. Veg. et de Bot. tome 1 page 49.)
(**Footnote. Id. tome 1 page 314.)
(***Footnote. Id. loc. cit.)
In the same year, M. Auguste de Saint Hilaire,* shows that the micropyle is not always approximated to the umbilicus; that in some plants it is situated at the opposite extremity of the ovulum, and that in all cases it corresponds with the radicle of the embryo. This excellent botanist, at the same time, adopts M. Turpin's opinion, that the micropyle is the cicatrix of a vascular cord, and even gives instances of its connexion with the parietes of the ovarium; mistaking, as I believe, contact, which in some plants unquestionably takes place, and in one family, namely, Plumbagineae, in a very remarkable manner, but only after a certain period, for original cohesion, or organic connexion, which I have not met with in any case.
(*Footnote. Mem. du Mus. d'Hist. Nat. 2 page 270 et seq.)
In 1815 also appeared the masterly dissertation of Professor Ludolf Christian Treviranus, on the development of the vegetable embryo,* in which he describes the ovulum before fecundation as having two coats: but of these, his inner coat is evidently the middle membrane of Grew, the chorion of Malpighi, or what I have termed nucleus.
(*Footnote. Entwick. des Embryo im Pflanzen-Ey.)
In 1822, Mons. Dutrochet, unacquainted, as it would seem, with the dissertation of Professor Treviranus, published his observations on the same subject.* In what regards the structure of the ovulum, he essentially agrees with that author, and has equally overlooked the inner membrane.
(*Footnote. Mem. du Mus. d'Hist. Nat. tome 8 page 241 et seq.)