316 Remarks on the Impregnation of Plants. 
of the ‘ovules. Prof. Amici* has, however, recently announced 
that he had in several instances traced the pollen-tubes them- 
selves quite into the cavity of the ovary ; from which he infers that 
the immediate contact of this body with the mouth of the ovule 
takes place whenever impregnation is effected. 
Jn the autumn of the year 1831, Dr. Brown read before the Lin- 
nean Society of London his highly interesting memoir on the Or- 
gans and mode of Fecundation in the Orchidea and Asclepiadee ; 
which has since been published in the last volume of the transac- 
tions of that society. It is unnecessary for our present purpose to 
indicate the several curious and important results of the investiga- 
tions of that sagacious botanist, relative to the structure and impreg- 
nation of these two families. He followed the course of the pollen- 
tubes, in several plants of both orders, from the stigma to the placenta, 
and in a single instance traced, in an Orchideous plant, some tubes 
or vessels of equivocal nature quite into the aperture of the ovule. 
r. Brown remarks that these tubes had been noticed in the style 
and ovary of these two families many years previous to his observa- 
tions, viz. in Orchideous plants by Du Petit-Thouars as early as 
1816 or 1818; and by the late Mr. Elliott in Podostigma, (a genus 
of Asclepiadez,) as stated in the first volume of the Sketch of the 
Botany of South Carolina and Georgia, published in 1817. Mr. 
Elliott adds that Dr. Macbride (since deceased) had observed the 
same fibres or cords in the style of some species of Asclepias. We 
have no reason to believe that in any of these instances the true ori- 
gin or office of these cords was even suspected. 
In a short communication addressed to the editor of the Linnea, 
dated Nov. 1827, and published in the fourth volume of that work, 
Dr. Ehrenberg gives an account of his observations on the structure 
of the pollen-masses in Asclepiadew ; and states that each grain is 
furnished with a cauda or cylindrical tube of great length, directed to 
the point where the membrane of the pollen-mass opens; which 
appendage he considers as analogous to the boyau, or pollen-tube of 
Amici and Brongniart.t He supposes that these processes exist 
previously to the application of the pollen-mass to the stigmatic sur- 
face, which is doubtless incorrect; but Dr. Brown has observed in 
tract from a letter from Prof. Amici to M. Mirbel, arte 3d July, 1830, 
ed published i in the 21st vol. of the Annales des Sciences Naturelles. 
+ Linnea. IV. 
