2^.8 



MOSSES AND FERNS 



CHAP. 



between them and the sterile tissue of the sporangiophore is 

 much more evident. 



The cells lying outside of the archesporium divide rapidly 

 both by longitudinal and transverse walls, and form the thick 

 outer wall of the sporangium. In longitudinal sections, two 

 rows of cells may be seen extending from the mass of arche- 

 sporial cells to the periphery. In these rows the vertical walls 

 have been more numerous than in the adjacent ones, so that 



7 ic. i2-L.—Oj>hioglossumfiendiilutn {I..). A, Young sporangium in longitudinal section, X22S. The 

 archesporial cells are shaded, the double line of cells shows where the sporangium opens ; B, part 

 of the sporogenous tissue from an older sporangium, X 225 ; C, cross-section of a nearly full-grown 

 sporangiophore, X15. 



the number of cells in these rows is greater. It is between 

 these rows of cells that the cleft is formed by which the ripe 

 sporangium opens. The cells of the ground-tissue adjoining 

 the archesporium divide into several layers of narrow cells, 

 which form the " tapetum." 



After the full number of cells is reached in the archesporium, 

 their walls become partially disorganised, and the cells round 



