220 



BOTANICAL GAZETTE 



[SEPTEMBER 



in the sporogenous mass up to the mother-cell stage, and then a 

 large growth of the sporangium walL When the spore mother cells 

 have rounded off and the tapetum has entered in between them, con- 

 ditions are good for the growth of these cells and the spores, which 

 then grow rapidly. Thus we have an alternating growth between 

 the sporangium w^all and the spores, which relieves the nutritive 



r 



Strain. 



The wall. — The outer wall of the sporangium is formed mostly 



I 



from the cap cell {figs, ji, 32). The first wall formed in the'cap cell 



c 



Fig. 31. A section showing the cells derived from the 

 cap cell arched over the sporangium from c to c, X 980. — 

 Fig. 32. A section of a sporangium somewhat older than 

 the one shown in fig. 31. X980. — FiG. 33. A section of a 

 sporangium, cut parallel with the surface of the leaf, showng 

 the first division of the cap ceU. X 980. 



is said by Praktl to be parallel with the leaf surface, but I find 

 that its position varies. Fig. jj is from a section cut parallel wnth the 

 leaf surface and it is here seen that the first wall is perpendicular to 

 plane of the lamina. 



The annulus appears as a circle of cells, one to three cells wide, 

 on the costal side of the sporangium {figs. 2g, jo). These cells become 

 much elongated in the direction of their axes, which are parallel with 

 the sporangium wall and with the cell w^alls which separate them one 

 from the other. This development gives the sporangium a beaked 

 appearance. The ring is widest on the upper side, where the thick- 

 walled cells of the annulus extend out along the sides of the stomium, 

 which is perpendicular to the annulus and in the median plane of the 



« 



sporangium 



On the upper side the ring is three cells wade; on 



o 



