22 DUNCAN, ON THE IMPREGNATION 
According to the previous turgidity of the terminal cell of 
the pollen-tube, so is the amount of pushing inwards which 
the embryo-sac-wall suffers, and the more rounded does the 
end of the pollen-tube become (fig. 6, a, y). 
It must be distinctly understood that no foxiemtiea of the 
embryo-sac occurs; that the pollen-tube presses the sac 
inwards, and produces, as the finger does upon a bladder, a 
concave depression ; and that the pollen-tube swells out from 
a vis a tergo, and fills the whole of this artificial depression. 
If the pollen-tube be pulled out of the canal of the micropyle 
its very shortness will tend to disprove the idea that it per- 
forates the embryo-sac. 
Twenty-four hours after impregnation, and forty-eight 
hours after the application of the pollen-grain to the stigma, 
the terminal cell of the pollen-tube—z. e. that im contact 
with the embryo-sac—is found to be nearly empty. The 
anterior surface of the embryo-sac, which was in contact 
with the end of the pollen-tube, is perfectly identical, in its 
overlapping cell structure, with the rest of the sac; but 
within the sac,in its former cell-less, granule-less contents, 
a change has occurred. After this time the pollen-tube 
decays. 
IV.—The appearances of the embryo-sac and the non- 
granular plasma within it, in the flower whilst in bloom, but 
before impregnation, have been noticed; the overlapping, 
circular, or ovoid cells of the sac, each with a distinct nucleus, 
are most delicate, and the simplest pressure will cause them 
to take on various forms or to rend. After the contact of 
the cell-wall of the pollen-tube, the ceils of the embryo-sac 
being pressed in upon the fluid contents of the sac, and 
yet not ruptured, suffer great flattening, and this must also 
be the case with the end of the pollen- tube. The trans- 
mission of the contents of the last or ultimate pollen-tube- 
cell—its fluid plasma and granules—from the interior of the 
tube-cell to the interior of the embryo-sac, is effected very 
shortly after the contact of the end of the tube-cell with the 
small cells of the embryo-sac; and in a few hours the 
contents of the embryo-sac have become granular, whilst 
’ the pollen-tube’s last is empty cell (fig. 9, e). If the 
pollen-tube be forced out of the canal of the micropyle 
forty-eight hours after the pollen has been added to the 
stigma, and the nucleus, with its large embryo-sac, submitted 
to the compressorium, under the lowest power of the micro- 
scope, and then the anterior part of the embryo-sac examined 
with the highest powers, it will be seen to be intact, to have 
