FORMATION OF CELLS— TISSUES 



309 



endosperm of Plimierogams. When this takes place, the nuclei 

 become arranged in a single layer over the internal surface of 

 the megaspore ; protoplasm aggregates round each nucleus, and 

 a common cell- wall is formed between each two adjacent cells, 

 separating them from each other. Their surface which is towards 

 the cavity of the megaspore remains for a little while naked, but 

 soon they secrete each for itself a cell- wall over it, thus forming a 

 peripheral layer of closed cells round the canty of the megaspore. 



FlO. 665. FiCf. 666. 



F/(/.665. Formation of zoogonidia in. 4 c^Z/w. 

 A. Zoogonidangium, still closed. B. The 

 same burst, with the discharged zoo- 

 gonidia. After Carpenter.^— Fig. 666. 

 a,'b. Escape of the swarm-spores of an 

 (Edogonium. c One in free motion. 



D, The same after it has become fixed, 

 and has formed the attaching disc. 



E. Escape of the whole protoplasm of a 

 germ-plant of (Edogonium in the form 

 of a swann-spore. After Pringsheim. 



Further multiplication of the cells takes place by repeated 

 cell-divisions till a mass of tissue fills the spore. 



The formation of the special mother-cells of the spores, 

 described above as a variation of cell-division, is often included 

 under free cell-formation. 



The principal, difference between the two modes is that in 

 free cell formation the new cell, if clothed at all, is nearly or 

 quite surrounded by a freshly secreted cell- wall ; in cell-division 

 a new wall is only formed across the line of the division. 



2. Formation of New Cells without Division. — Two 



