CUTICLES OE Cy CADE AN FEONDS. 



177 



w 



In Bowenia and Stangeria, where the guard-cells are not^ sunk, there are from four 

 to six subsidiary cells, differentiated into polar and lateral (text-fig. 1 ; PL 17. figs. 1, 

 7, & 8). Occasionally there is some displacement of the cells, so that the differentiation 

 is not always quite definite (text-fig. 1; PL 17. fig. 8). Encephalartos (text-figs. 7 

 & 8), Ceratozamia (text-fig. 12; PL 18. fig. 2), Macrozamia (text-figs. 15 & 16), and 

 Zcmia (text-figs. 21 & 22) typically show from four to six subsidiary cells, differentiated 

 into polars and laterals. An interesting distinction in Zamia is the frequent presence 

 of a second series of lateral subsidiary cells, parallel with the first, due perhaps to the 

 longitudinal division of the original lateral cells * ; this is well seen in Zamia Lindeni 

 (text-fig. 21). The subsidiary cells in these four genera are at a different level from that 

 of the guard-cells, the latter being sunk to a greater or less degree, forming an outer 

 air-space. The opening of the air-space at the surface of the leaf is elliptical to quad- 

 rangular in shape. In some cases, particularly in some Macrozamias and some species 

 of Encephalartos, there is a certain amount of overarching of the subsidiary cells. In 

 cases where the guard-cells are much sunk, the opening of the air-space on the leaf- 

 surface is more rounded in shape, and the subsidiary cells, which tend to increase in 

 number for the better strengthening of the large air-space, are not distinguished into 

 polars and laterals. This is seen in Dioon and Cycas revoluta, where all the cells are 

 of the same shape. Occasionally also the subsidiary cells are raised beyond the general 

 level of the epidermis, forming, small elevations perforated by the stoma - openings 



(PL 17. figs. 12 & 13, Oi/cas revoluta). 



In some cases crystals of calcium oxalate occur in the epidermal layers ; in Stangeria 

 they are to be found in the cells round the stomata ; in Macrozamia cylindrica crystals 

 occur on the upper leaf-surface and on the lower surface in the cells of the nerve- 

 courses. In other cases, e.g. Dioon edule and Macrozamia spiralis (=Fraseri?), they 

 occur in spaces between the epidermal cells. 



Hair-scars occur in several cases, such as Encephalartos Ghellinckii, Cycas circinalis 



and C. revohita, Zamia integrifolia and Stangeria. 



The cutin layer overlying the epidermal cells is fairly thick-usually thicker on the 

 upper than on the under side of the leaf. Dioon, Ceratozamia, and some species of 

 Encephalartos show the heaviest cutin layer, while that of Bowenia is comparatively thm. 

 The cutin of Stangeria has very characteristic folds. 



III. CUTICLES OF FOSSIL CYCADEAN FRONDS. 



(a) Previous Observations on the Cuticular Structure of Fossil Cycadean Fronds. 



Bornemann, whose work has been mentioned above, was the first to make observations 

 upon the structure of the cuticles of fossil fronds, and, in fact, made a comparative study, 

 based on the recent forms, of a type which has never since been attempted (1856). The 



Cf. Takeda (1913 >), p. 351 ; (1913^), pp. 365, 3G6 ; text-fig. 8. 



