AND ON POLYEMBRYONY IN THE HIGHER PLANTS. 5 
bum a naked nucleus occurs, out of whose apex the embryo-sac 
grows forth quite freely, and advances to meet the pollen-tube ; 
here, then, that happens quite regularly which I have observed 
merely exceptionally in Phaseolus, namely, that the apex of the 
embryo-sac serves immediately as a micropyle for the reception 
of the polien-tube. 
But this union of the pollen-tube with the apex of the em- 
bryo-sac is the very act of impregnation; and I have observed 
it under the following perceptible phenomena. There in some 
cases originates after the union of the pollen-tube with the apex 
of the embryo-sac, probably by the reciprocal dynamical action, 
a small protuberance at the place of the union, which grows 
larger and larger, fills with a turbid, slimy substance, and 
separating itself from the pollen-tube, becomes a vesicle, which 
very soon expands in length, and grows deeply into the em- 
bryo-sac. I have called this vesicle the germ-vesicle; it is the 
first product resulting from the sexual action which the pol- 
len-tube exerts on the apex of the embryo-sac, and we shall 
subsequently see how the substratum for the embryo ori- 
ginates from this germ-vesicle. The most usual case which 
we observe in the process of impregnation, is, however, that 
where the germ-vesicle originates in the interior of the embryo- 
sac; and this again takes place in two different kinds of union 
of the pollen-tube with the embryo-sac; either the pollen-tube 
coheres directly by the apex of its extremity with the apex of 
the embryo-sac, or, which indeed is the more rare case, the 
extremity of the pollen-tube applies itself laterally to the apex 
of the embryo-sac. In this latter case the origin of the germ- 
vesicle is usually very easy to observe, and, at the same time, 
these cases are the most decided proofs against the doctrine 
that the embryo-sac is indented by the entering pollen-tube in 
order to help in forming the embryo. In some species of the 
genus Mesembryanthemum I have found this lateral union of 
the pollen-tube with the embryo-sac quite constant, and have 
already published some drawings of it*; but recently I have ob- 
served this process very minutely in Mesembryanthemum pome- 
ridianum, and have made from it the accompanying drawings 
(Plate II. figs. 7-14). In both cases of the union of the pollen- 
tube with the embryo-sac, a perfect cohesion first takes place, 
quite similar to the conjugation of some Conferve, and soon 
* Meyen’s Vegetable Physiology, vol. iii. pl. xiii. figs. 46 and 47. 
