5 i8 



FILICALES 



marked a feature in Ferns at large that these irregularities command the 

 greater attention. Fig. 286 A represents a tangential section traversing 

 three sori in Danaea elliptica, of an age prior to the tetrad-division : the 

 varying size of the sporangia is striking, as also their frequent grouping 

 in pairs, separated by a thin, or even by a partial septum. Some of 



r 



I. 





</WKI$ 

 /,;^ihw b 



D 



Km. 



Dmiaca ellifitica. Smith. Drawings illustrating partial septations of the sporangium. 

 A, tangential section through three sori, showing the loculi in ground plan : the sepia are 

 often thin, so that pairs of loculi are in close juxtaposition ; the loculi marked (.r) 

 are large, and show one or more partial septa. X 20. B, C, /?, fi, show such loculi with 

 partial septa in greater detail : in /' anil /: it is difficult to decide whether the cells 

 marked (?) will develop as tapetum or as spore-mother-cells. X 150. 



in 



these partially septate sporangia are represented more in detail 

 Figs. 286 B-E. From these drawings it is clear that the identity of the 

 sporangium is not maintained : that where the initial sporogenous group 

 is large, some of its cells may develop as transitory tapetum, or even as 

 permanent cells of septal tissue : and thus various intermediate steps of 

 completion of a septum may be observed. Somewhat similar conditions 



