182 



3IR. H. HAMSHAW THOMAS AND MISS N. BAKCEOFT ON 



and in tlieir relations to the subsidiary cells, with the thickenings of Stang 



seen 



after maceration (see text-fig. 32) 



The "figures below (text-fiff. 28) show an attempt to 



the sectional views of the stomata at various points in accordance with the 



explanation given above. 



Fisr. 28. 



-l- A 



B 



I. 



i 



II. 



Diagrams representing surface view of stoma of Stangena (I.), with hypotlietical 



sections (II.) at the different points indicated in I. The shaded and dotted 

 portions represent the probable positions of the thickened portions. 



In some modern stomata we find that the upper lamellae do not extend unchanged 



the pore, but the latter is 



anded by a thinner oval area. A precisely similar 



rangement is seen in some of the PtilopJiyllum and Zamia cuticles (see PI. 19. fig. 2). 



Unfortunately, it has proved impossible to obtain sections through the cuticles 



a comparison of the material 

 before us with the stomata figured by Lignier provides some interesting features and 

 gives considerable support to the interpretation just advanced. In his paper on 

 Bennettites Morierei, Lisrnier * observed that in some sections through the involucral 



showing the structure of these stomatal remains, but 



bracts, the stomatal guard-cells 

 figures, PI. 1. fis. 9, which is re 



o 



o 



, cut through transversely, were seen. In 

 produced below (text-fig. 29), two stomata 



of his 

 Seen in 



Fig. 29. 



Section through the epidermis of a bract of Bennettites Morierei showing two stomata cut through 

 The characteristic form of the guard-cells and subsidiary cells is well shown. (After Lignier.) 



The 



guard - cells are 



section cut through transversely somewhat near their poles, 

 seen to have the pear-shaped outline, so characteristic of the modern forms {cf. text- 

 figs. 26, etc.), with a marked upward extension. The upper walls of the guard-cells 



are drawn as being somewhat thickened, the wall abutting on the 



slit 



being 



thin; 



* 



Lignier (1894), p. 18, pi. 1. figs. 8, 9. 



