264 Mr. J. 8S. Sanderson on the Embryogeny 
session of which the researches of Unger, Hofmeister, and Tulasne 
have put us, we need be at no loss to arrive at certain general 
conclusions as to the order im which the various steps of the em- 
bryogenic process are brought about, and the laws by which it is 
governed. We shall therefore occupy the remainder of this 
paper in enumerating as shortly as possible the most important 
of these generalizations. 
In order to facilitate description, we shall divide what seem to 
be the essential phenomena of the embryogenic process in the 
higher plants into three classes, m the first of which we shall 
consider the process of development of the embryo-sac ; in the 
second the changes which take place within the embryo-sae be- 
fore, and in the third, after the act of impregnation. 
We shall first speak of the development of the embryo-sac, or 
the individualization of a cell of the female organ for reproductive 
purposes. 
At a very early period a constituent cell, of what is called in 
descriptive language by a singular misnomer the placenta, gives 
rise by successive division to a cylindrical body, which consists 
of a central series of cells surrounded by others of smaller size. 
This, by another equally obvious misnomer, is called the ovule. 
From the central series of cells just mentioned one is separated 
and set apart for reproductive purposes, while the rest are va- 
riously developed so as to form coverings to this one. It enlarges 
at the expense of the rest, and receives the name of embryonal 
sac, and 1s strictly analogous to the animal unimpregnated ovum. 
We next consider the changes which take place in the cavity 
of the embryo-sac previous to impregnation. 
At a period considerably prior to impregnation a vesicle is de- 
veloped, always at the micropyle-end of the embryo-sac, and pro- 
bably always from acytoblast. This vesicle enlarges more or less, 
and contains a fluid granular protoplasm. To this the name 
embryo-vesicle is assigned. It is analogous to the germ-vesicle 
in animals, both in its production and subsequent development. 
Besides the embryo-vesicle other cells are freqaently developed 
at this period, which are destined to conduce to the nutrition of 
the future embryo. 
Lastly, we have to consider the changes which take place m 
the embryo-sac after impregnation. 
At this period a cell belonging to the male organ (the pollen- 
grain) becomes so developed that its membrane and that of 
the embryo-sac are brought in contact ; in consequence of which 
an interchange of their “contents takes place, and under the pe- 
culiar influence of the one upon the other, the embryo-vesicle 
begins to develope within it two cells divided from each other 
by. a transverse septum, in the same way as the first change ob- 
