CUTICLES OF CYCADEAN FRONDS. 



161 



^J 



r r 



less regularly-disposed pores, which occur principally towards the periphery 



of the cells and which 



ered by the 



lay 



This pitti 





both 



upper and lower epidermis, and is not known to be present in any other genus of the 



^ 



wer 



Cycadacese 



the largest 



the lateral walls also 



marked in C. revolutc 



The pores vary considerably 



size in 



the differ 



pecies of Ci/ 



observed in (7. circinalls 



smallest 



(7. MicholitziL Pitting of 



rs, but in a varying degree (PI. 17. figs. 10 & 13 

 C. undulaia, however, pits occur only here and t 



It 



Fig. 2. 



Fiff,3 



Cycas Mi 



Lower cuticle in surface view : 



5, a stoma- opening, surrounded by six subsidiary 



The thickened appearance round the 



cells. 



due to the showing-through 



stoma-opening is 



of the cutin layer 



overlying the guard- cells, X 450. 



lining the air-space 



and 



Cf/cas revoluta. — A stoma iu surface view, focussed 



. below the level shown in PI. 17. fig. 12, so that 



the dorsal or upper surfaces (d) of the guard-cells 



are seen surrounded by fifteen small cells, the 



intercalated series shown in section in PI. 17. 



fig. 13. 



X 450. 



Stomata occur only 



underside of the piniice, and are scattered and 



position 

 Cycas fall 



As both Bornemann 



and Kraus liave ^jreviously mentioned, the species of 

 ronps, according to their epidermal and stomatal characters, which, 



The first group 



th 



e 



moreover, correspond with the external characters of the leaves, 

 species such as C revoluta, with narrow pinnse, the margins of which are inrollcd f 

 second group, of which C. circmalis is an example, contains species with broader, flatter 

 pinn^, less xerophytic in texture than those of the first group. All the types examined, 

 with the exception of C. revoluta, belong to this group. 



In the first type the epidermal cells are irregular in shape and disposition, particularly 



on 



the under side of the pinnae, where, however, they 



diameter often lies transversely to the pinna 



more isodiametric 



their 



The most distinctive featur 



of the cuticle consists in the complication of the stomatal apparatu 



The guard -cells 



well sunk below the surface, and between them and the subsidiary cells, which 



d-cells and form an " outer air-space," is an mtercalatcd 



small cells (PL 17. fig. 13; text-fig. 3 J). 



case overarch the guar 



consisting of from twelve to fifteen 



n\ 



These 



* Microcycas has uot yet "been examined. 



t Bornemann and Kraus have also examined C. inermis in this group 



Cf. Kraus (1866), Taf. 19. figs. 4 & 5. 



