264 Mr. /. S. 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 in 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 phsenomena of the embryogenic process in the 

 higher plants into three classes, in 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-sac 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 jjlacenta, 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 is 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 a cytoblast. 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 frequently 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 in 

 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 • 



