RKJUVENKSCENCE IN NATURE. 167 



off from the decay commencing in another part, by a 

 sharp line of demarcation, and of coating this boundary 

 with cell-membrane. 



The constitution and defined material isolation of the 

 cell before the formation of the cell-membrane, has been 

 observed in the free formation of the germ-cells of the 

 Phanerogamia, as well as in the germ- and seed-cells of 

 many Algae. According to Wilhelm Hofmeister's re- 

 searches on the Origin of the embryo of Phanerogamia,* 

 researches widely extended and carried out with admirable 

 acuteness, — after the formation of a few nuclei the proto- 

 plasm accumulated in the end of the mother-cell of the 

 germ-cells (the embryo-sac) next the micropyle, divides 

 into two or three longish^ rounded balls, each of which 

 encloses one of the nuclei. These balls display no trace 

 of a cell-membrane in their earliest condition, and when 

 they lie long in water, fall away into an amorphous semi- 

 fluid mass ; but they very soon become coated with a 

 cellular membrane, and then are no longer liable to 

 destruction, even from a long-continued action of water. 

 These cells formed free in the contents of the embryo-sac, 

 are the first rudiments of new plants, the germinal 

 vesicles, as they are termed, only one of which is usually 

 developed, through fertilisation taking place subsequently 

 to their formation. 



That which does not admit of doubt, in the cases just 

 considered, where it is possible to observe the pro- 

 cesses on the free surface of newly formed cells, namely, 

 the secondary production of the cell-membrane around 

 the already existing and defined body of contents of the 

 cell, must certainly hold good also of those cases where 

 the division of a mother-cell into two daughter-cells is 

 apparently effected through the formation of a mem- 

 branous septum. If it be once certain that the cell- 

 membrane is formed by secretion on the surface of the 



* Vide Hofmeister, 'Der Ensteliung des Embryos der Phauerogamen,' 

 (1849), p. 4. et seq. 



