53 



Fig. 90. Ceratopteris siliquosa. Sections through acetolyzed sclerine. The 

 sclerine, as shown in b, consists of a thin perine (the outermost gi'anular 

 layer) and a thick exine faintly sulxlivided into cf. sexine (showing + 

 parallel ridges separated by U-shaped valleys) and cf. nexine (of equal 

 thickness throughout). The upper figure (a) intimates that the sexine has a 



fine (granular) structure, x 700. 



CETERACH:— 



a b c d e 



Fig. 91. Ceterach officinariim. From left to right: proximal face (x 250); 

 sclerine sti-atification (x 2000); lateral, longitudinal view (x 1000); LO- 



patterns. 



