Origin and Development of the Vegetable Embryo, 61 
From the preceding statements we gather the following gene- 
ral statement of the process of impregnation. 
At the period of the opening of the flower the embryo-sac ex- 
ists, and at its upper (micropyle) end one or more cells (germinal 
vesicles) are produced from cytoblasts. The pollen-tube makes 
its way down the style into the ovary, and finally through the 
foramina of the coats of the ovule, and comes in contact with the 
embryo-sac ; here it either applies itself immediately upon the 
apex or proceeds a little way further, so as to lie rather on the 
side of the apex of the embryo-sac. Hereupon (and probably as 
a result of the imbibition of the fluid of the pollen-tube through 
the membranes) the cell, or one of them if there are more, lying 
in the embryo-sac, begins to develope, and in course of time 
produces the embryo. 
We may glance at the evidence to be obtained from the accounts 
given by authors who deduce conclusions difl’erent from the above. 
Meyen* believed that the phsenomena presented themselves with 
two modifications ; the first where the embryo-sac evidently exists 
before impregnation, and the second where, as he believed, this 
is wanting at that period. The latter modification, where he said 
that the germinal vesicle is produced by the end of the pollen- 
tube, cannot be brought into relation with the theory under exa- 
mination, but the latter presents some points of resemblance. In 
this case he stated that the pollen-tube comes in contact with 
the embryo-sac and becomes united with it, and then the ger- 
minal vesicle makes its appearance in the embryo-sac. But in 
one instance which he figured, namely in Mesembryanthemum glo- 
merutum\y he confessed that the absorption of the membranes 
separating the cavities of the pollen-tube and embryo-sac was an 
assumption, and the figure in question exactly resembles Miiller^s 
representation of the phsenomenon, the pollen-tube lying rather to 
the side of the summit of the embryo-sac. If we could believe 
that he was mistaken in supposing that an actual union of the 
embryo-sac and pollen-tube took place (and in such investiga- 
tions graver errors are easily fallen into), the only point of difter- 
ence would be with regard to the period when the germinal vesicle 
is first produced. 
In reference to Schleiden^s opinions, the view which he first 
promulgated was that the pollen-tube pushed the summit of the 
embryo-sac before it and became invested by ih but in the last 
edition of his ^ Grundziige he admits the possibility in certain 
cases of the actual entrance of the pollen-tube into the embryo- 
* Pflanzen-pbysiologie, vol. iii. 
-t Op. cit. vol. iii. pi. xiii. figs. 46, 47. 
I Grundz. dps Wiss. Botanik, 2nd edit. ii. 366. 
