478 



MOSSES AND FERNS 



CHAP. 



centre of the cell, and the connecting filaments are formed be- 

 tween them. In the connecting spindles there is formed be- 

 tween each pair of nuclei a cell plate, which soon develops into a 

 definite cellulose membrane, and the spores separate completely. 

 It is probable that the definitive cell-wall is formed in the 

 same way as in the spore- formation of other plants (Mottier 

 (3), p. ^2). The cell-plate formed at the equator of the spindle 

 in the later stages of division, is split into two layers which thus 



B 



m. 



Fig. 280. — A, Group of sporogenous cells, just before the final division into the spores, 

 embedded in the nucleated protoplasm formed from the disintegrated tapetum, and 

 sterile archesporial cells, X500; B, optical section of young spore, showing the 

 three membranes; m, the middle lamella, Xsoo; C, an older spore, showing the 

 splitting of the outermost coat to form the elaters, X500; D, surface view of the 

 dorsal cells of the wall of a ripe sporangium, X150; E, section of the wall, show- 

 ing the remains of the inner layers of cells (0> X250. 



separate completely the two protoplasts. In the space between 

 the protoplasts, the new cell-wall is then laid down. 



The young spore has at first a very delicate cellulose mem- 

 brane, which thickens, and later has separated from the outside 

 the ''middle layer" (Fig. 280, B, m), which in spores placed in 

 water lifts itself in folds from the underlying endospore. The 

 outer perinium seems to be unquestionably formed through the 

 agency of the nucleated protoplasm, in which the young spores 



