166 ME. H. HAMSHAW THOMAS AND MISS N. BANCEOFT ON 



t 



text-fig. 10) (Porscli, 1905, Taf. 1. fig. 7). The cavities are lined with a layer of cutin, 

 and the epidermal cells surrounding the stoma-openings (subsidiary cells) arch over 

 slightly. They are also a little raised beyond the surface of the pinna, and are rounded, 

 as seen in surface view. They are from six to eight in number and are much thickened, 



especially in I), edule (text-fig. 9). 



Crystals of calcium oxalate occur in D. edule on the lower side of the pinnse in the 

 nerve-courses. They were not observed on the upper side. Kraus figures a crystal 

 from the lower epidermis, but does not specially note their occurrence there. He 

 mentions that "here and there a thin-walled cell contains a crystal." So far as could 

 be determined, however, from the appearance in surface view and in section, the 

 crystals occur in cavities or spaces between the cells rather than in the cells themselves 

 (PI. 18. figs. 8 & 9} ; for in surface view the rounded ends of the neighbouring cells 

 seem to project into a space, and in section Scharlach R shows the presence of a layer 

 of cutin entirely surrounding or lining the crystal-containing space.* D. spinulosimi 

 has no crystals. 



The cutin layer in both species is very thick, especially in I>. edule (PI. 18. 



figs. 7 & 



Ceratozamia, Brongn. PI. 18. figs. 1-4 ; text-figs. 11 & 12. 



Refekences: — Bornemann (1856) 



Taf. 21. figs. 17-20. Mahlert 



12. figs. r-10. Kraus (1886), pp. 38, 39; 



Species examined : — C. mexicana, Brongn. ; C. fusco-viridis, D. Moore; C latifolia, Miq. 



These three species show the same general characters, all possessing two kinds of 

 epidermal cells, thick- and thin-walled. The thick-walled cells apparently predominate 

 in Ceratozamia (cf. Dioon), though they are somewhat variable in number and in dis- 

 tribution in the three species examined. There is considerable variation, moreover, in 

 the relative thickness of the thick-walled cells ; C. mexicana shows a very marked 

 contrast between the two kinds of cells (PI. 18. figs. 1 & 3) ; C. latifolia shows com- 

 paratively little difference between them (text-fig. 11); while C\ fusco-mridis is inter- 

 mediate in this respect. The cells — ^particularly the thicker-walled ones — are much 

 elongated in the direction of the longitudinal axis of the pinna. The cells of the 

 nerve-courses, in the lower epidermis, are similar to those of the upper side; while 

 between the nerve-courses, as is usual, tlie cells are shorter and broader. Thin-walled 

 cells occur in these areas also, especially in G. mexicana (cf. Dioon). 



In C. latifolia, the elongated thick- walled cells of both upper and lower epidermises 

 are often septate (text-fig. 11) ; Kraus notes the same fact in C. Xmteriana, 



C. mexicana shows pitting on the lateral walls of the thickened cells (PL 18. figs. 1 & 2). 

 This is more marked on the lower surface than on the upper, especially in the case of 

 the subsidiary cells of the stomatal apertures. In C. fusco-viridis also, the lower 

 epidermal cells are much pitted ; in 0. latifolia, however, pitting was not noted, except 



* A similar occurrence of crystal-containing cavities 13 quoted by Nestle r in the case of Encejyhalartos cafer. 

 In D- edule the cavities are apparently larger than in that species. 



