2 MEYEN ON VEGETABLE IMPREGNATION 
hypothesis on the sexes of plants, and have refuted it, at least 
in my opinion, by some decided proofs ; but since I have learnt 
that some persons have misconceived my observations on the 
act of impregnation in plants, I take up the subject once more, 
and, bringing together the main results of my former inquiries, 
I shall combine them with my recent observations, and at the 
same time avail myself of the latest researches of other botanists. 
Berlin, October, 1839. J. MEYEN. 
IT has been seen that the doctrine of the difference of sex 
in plants was so generally and firmly established by the produc- 
tion of hybrid plants, that a long period has elapsed before even 
a doubt has been ventured against the adoption of this differ- 
ence of sexes similar to that of animals. The writings of Schel- 
ver and Henschel were, each in its peculiar way, to have laid 
open our error on this subject ; but already a short period has 
pronounced judgement upon them, for they themselves are 
now but of historical interest, and precisely through the means 
of these writings a more accurate confirmation of the doctrine 
of the separate sexes of plants was brought about. From this 
period greater care was employed in observing the plastic pro- 
cess which occurs in the impregnation of plants, and we arrived, 
by the united discoveries of Amici, Brongniart, Robert Brown 
and many others, at the result that the fructifying substance in 
phznogamous plants is carried from the interior of the pollen- 
grain through a peculiar tube, the pollen-tube, into the cavity in 
which the production of the embryo, or the substratum for the 
future plant, takes place. An accurate historical exposition of 
the progress of these discoveries will be found in the last volume 
of my Vegetable Physiology, to which therefore I may refer. 
In the year 1837, however, Professor Schleiden brought 
forward a new view on the subject of the sexes of plants; he 
worked under the special guidance of his uncle, our honoured 
and celebrated Professor Horkel, and how much of this new 
view belongs to the latter is, it is true, not known to me ; but of 
this I am aware, that Professor Horkel was acquainted with the 
plastic processes in the impregnation of plants long before the 
appearance of the celebrated memoir,of Brongniart, and, indeed, 
frequently more accurately than they are represented in that 
memoir. MM. Horkel and Schleiden believe that the passage 
of the pollen-tubes from the stigma to the ovulum, is the general 
