174 MR. H. HAMSHAW THOMAS AND MISS N. BANCEOFT ON 



thin pear-shaped areas in the thickened area overlying the guard-cells. The projectio 



lamellae 



of thickening material formed hy the extension of the ventral lignified 

 at the poles of the stoma (see text-fig. 26, showing the correlation of serial sections 

 through a stoma with the surface view). The cutin layer overlying the lamellae is 

 faintly striated as in the case of Stangeria (PL 17. figs. 7 & 8). 



Neither hair-scars nor crystal cavities were ohserved. The cutin layer, compared 

 with that of the other genera, is not very thick (PL 17. fig. 9 ; text-fig. 24). 



(iii .) General Summary of the Structure of the Recent Cuticles. 



The epidermal cell's of Cycad leaves have usually slightly curved or straight walls. 

 Stangeria has undulate walls somewhat like those of ferns*. The walls generally 

 attain a considerahle thickness, and often show layering as in Ceratozamia, Dioon, and 

 some Macrozamias. Bowenia has comparatively thin walls, while Ceratozamia and 

 Dloon on the whole have the tliickest, though these are characterised by the possession 

 of two kinds of epidermal cells, some elongated and thick-walled, and others shorter and 

 thin-walled. A variation in the thickness of the walls occurs also in Macrozamia, some 

 Zamias, and to a certain extent in Enceplialartos. The epidermal cells are usually 

 elongated, and in Cycas and Stangeria are alike on both upper and under sides of the 

 leaf. In other types the cells of the under side following the course of the veins are 

 similar, or nearly similar, to those of the upper side, while the general epidermal cells 

 between the " nerve-courses " are more isodiametric. Usually, in the upper epidermis, 

 the nerve-courses are not marked by any difference in the form of the epidermal cells ; 

 Stangeria shows a slight elongation and narrowing of the cells above the veins. 



Stomata occur generally only on the under side of the leaves between the nerve- 

 courses, their long axes coinciding or forming a slight angle with the long axis of the 

 pinnae. The occurrence of stomata in these definite areas seems to be correlated with 

 the above mentioned diff'erence in the form of the epidermal cells there, as compared 

 with those of the nerve-courses (see Zamia, Macrozamia, Ceratozamia, Dioon, and 

 Encephalartos). In Cycas and Stangeria the stomata are scattered and irregularly 

 placed ; there are no fixed stomatal areas. 



Bornemann (1856, p. 42) has recorded the occasional occurrence of stomata on the 

 upper side of the pinnae in Zamia muricata var. pieta. Kraus (1866, tig. 15) figures 

 a stoma of the pinna-base in Enceplialartos Altensteinii ; it is apparently from the 

 upper side, though he does not mention the occurrence of stomata other than on 

 the under side of the pinnse. Nestler (1895, p. 362) was unable to find such stomata 

 in Bncephalartos ; in JBoicenia, however, he records them from the basal parts of the 

 upper side of the pinnules, gradually decreasing in number and finally disappearin 

 towards the middle. The present investigations have revealed the presence of stomata 



on the upper side of the pinnse in Stangeria. They are, however, confined to the 



midrib (text-fig. 1). 



* Bornemann (1856), p. 42 ; Krau3 (1866), p. 13. 





