158 ME. H. HAMSHAW THOMAS AXD MISS N. BA^s^CEOFT ON 



{c.) Description op the Cuticles. 



(i.) Introduction. 



In a consideration of the cuticles* of recent Cycads with a view to comparing 

 them with those of fossil fronds, the features which seem to he of greatest value 

 are those which may he determined from an examination of surface views. The actual 

 form, size, and arrangement of the guard-cells, and the thickening of their walls as seen 

 in section, are very constant throughout the group, and the variations mostly depend 

 upon the appearance in surface view. The chief features to he taken into consideration 



are as follows : — ' , 



(1) The form and outline of the epidermal cells of upper and lower surfaces of the 



the pitting and thickness, straightness 



leaves, hoth hetween and over the nerve-courses ; 



or irregularity of the cell- walls. 



2) The distribution and position of the stomata, whether scattered or in definite 

 restricted areas ; whether irregularly placed or having their axes in a fixed direction with 



regard to the axis of the pinna. 



(3) The appearance of the stomata in surface view, depending upon the presence or 

 absence of an intercalated series of cells hetween the guard -cells and the general 

 epidermal cells, and the consequent degree of sinking of the guard-cells below the 

 epidermis ; the shape of the stoma -opening. 



(4) The number and arrangement of the subsidiary cells f (the epidermal cells 

 surrounding the stoma, or in the case of much sunk guard-cells, those around the stoma- 



opening at the surface of the leaf). 



(5) The presence or absence of crystals, either in the epidermal cells or in inter- 

 cellular spaces. 



(6) The presence or absence of hairs or hair-scars. 



(7) The thickness of the cutin layer, and the presence or absence of foldings or 



striations upon it. 



(ii.) Detailed Description. 

 Stangeria, T. Moore. PI. 17. figs. 1-6 ; text-fig. 1. 



Heferences :-Bornemann (1856), pp. 41, 45 ; Taf. 12. figs. 19, 20. Kraus (1866), p. 34; Taf. 23. 



figs. 28, 29. Nestlcr (1895), p. 363. 



The typical Stangeria paradoxa, T. Moore, and its variety scUzodon, were examined 

 and found to be exactly similar in epidermal and cuticular characters. The genus is 

 distinct from all other Cycads, in that the epidermal cells of both upper and lower 

 surfaces of the leaf-lamina have undulate lateral walls, like those of the epidermal cells 

 of f ?rns. These cells are irregular in form and arrangement, and are usually three- or 

 four-ano-ular. Over the midrib of the pinnae the undulations are absent, and the cells 



* The term <' cuticles " is used to include the layer of epidermal cells and the overlying layer of cutin 

 t " Wall-Zellen " or " iS'ebeuzellea " of the German authors. 



