DEVELOPMENT OF CELLS. 



589 



rated from the wall of the parent cell, so that the new cell is free 

 (or loose) in the cavity of the parent cell. 



Modifications of Free-cell Formation. These are numerous. 

 The simplest case is where the protoplasm, enclosing the ivhole con- 

 tents of the parent cell, separates all over from the wall of the 

 parent cell, and, while thus free, produces a cellulose membrane 

 over its whole surface, which constitutes the wall of a new cell. 



Fig. 594. 



Fig. 595. 



Development of the embryonal vesicle of 

 Santalum album. A. The upper end of the 

 embryo-sac, with the embryonal corpus- 

 cles ( e v) as yet devoid of cell-membranes. 

 B. The same later, with the pollen-tube 

 (p f) adherent : the embryonal vesicle (e v) 

 has acquired a cellulose coat. Magn. 400 

 diam. 



Development and fertilization of spores of 

 Fucusvesiculorus; a, inner spore-sac burst- 

 ing from the outer sac and about to liberate 

 the spores ; b, a free spore (devoid of cellu- 

 lose coat) surrounded by spermatozoids ; c, 

 impregnated spore with a cellulose coat ; d, 

 the same germinating. Magn. 160 diam. 



This takes place in the formation of the parent cells of the pollen, in 

 the cells of the parenchymatous tissues of the central region of the anther, 

 and sometimes, but not always, in the formation of the pollen-grains. It 

 appears to occur also in the formation of the parent cells of the spores of 

 Mosses, Hepaticse, Ferns, &c. If the separated protoplasm escape and 

 assume an independent career, the formation is by isolation or segregation, 

 as before explained. 



A case closely analogous to this is where the whole contends of the 

 parent cell become parted into four or more portions, collectively filling 

 the parent cell, but free from it, so that when they secrete their membranes 



