’ Scientific Reviews. 195 
of the generalizations to which these researches led, we constrain 
ourselves to a simple statement of what they profess to have seen, 
and a comparison of the points upon which they differ. 
As early as the year 1826, in the botanical appendix to Captain 
King’s Voyage to Australia, (Vol. II. p. 534,) Mr. Robert Brown 
had shown that the apex of the nucleus of the ovulum, the point 
which is universally the seat of the future embryo, was very gene- 
rally brought into contact with the terminations of the probable 
channels of fecundation,—these being either the surface of the pla- 
centa, the extremity of the descending processes of the style, or 
more rarely, a part of the umbilical cord. It also appeared, how- 
ever, from some of the facts noticed in the same essay, that there 
were cases in which the particles contained in the grains of the pol- 
len, could hardly be conveyed to that point of the ovulum, through 
the vessels or cellular tissue of the ovarium ; and the knowledge of 
these cases, as well as of the structure and economy of the anthere 
in Asclepiadez, led Mr. Brown to doubt the correctness of obser- 
vations made by Stiles and Gleichen, as well as more recent state- 
ments respecting the mode ef action of the pollen in the process of 
impregnation. ‘Fhese observations were confirmed by Mr. Raspail 
in the 14th volume of the Memoires du Museum d Histoire Natu- 
relle, in which essay the author also endeavoured to prove that the 
apparent perforation was owing to a transparency in the summit of 
the cylinder, towards which the radicle of the embryo probably di- 
rected itself. 
In 1827, in the 4th volume of the Memoires de la Societé d’ His- 
torre Naturelle, another essay of Mr. Raspail’s is inserted, in which 
he states his opinion, that the epidermis of the pollen incloses an- 
other vesicle, which is driven out by ammoniacal gas, and that this 
vesicle contains two or more glutinous and elastic vesicles, which 
sometimes lengthen themselves like an intestinal canal, and that it 
is to the coats of this intestine that the particles which are driven 
out by the explosion attach themselves. Mr. Adolphe Brongniart’s 
essay, On the Generation and the Developement of the Embryo in 
Vegetables, had been read by Mr. Alexandre Brongniart, in the 
last days of 1826, before the Academy of Sciences, and six months 
after, (June 1]. 1827,) Mr. Mirbel reported on the labour. In 
this report, after stating that the subject was not new, Mr. Mirbel 
says that it appears at present indubitable that fecundation does not 
take place by the vascular part of the style and the umbilical cord, 
but by the cellular tissue and the micropyle,—an important fact, 
announced by Mr. Morland, and which Mr. Robert Brown, and, 
after him, Mr. Brongniart, have placed in the highest degree of 
probability. The membranous mass, of cylindrical form, which 
Mr. Amici had observed to pass out of a grain of the pollen of Portu- 
laca oleracea, and, inclosing the fecundating granules, elongate it- 
self on the stigma, Mr. Brongniart ascertained not only to exist in 
that plant, but in many other phanerogamous species ; and proba- 
bly that in most it penetrated into the interstices of the cellular 
