THE EPIDERMIS. 



81 



covering them. Hence there remains only an elongated elliptical 

 pit (/) which leads to the stoma (Fig. 28, A). This stomatic pit 

 usually appears black, because filled with air. In order to see 

 the guard-cells well, now turn the section over. It can then 

 be easily proved that the stoma is enclosed between two semi- 

 lunar guard-cells. In distinction from the neighbouring epider- 

 mal cells these cells contain chlorophyll bodies. The nuclei 

 usually show as clear spots about the mid-length of the guard- 

 cells. Between the two guard-cells is a spindle-shaped cleft, the 

 stoma proper or stomatic cleft (s), apparently about half the 

 length of these cells. 



FIG. 28. Epidermis of the under side of the leaf of Iris ftorentina. A, surface 

 view ; , in cross section ; ./', stomatic pit ; s, cleft, or stoma ; c, cuticle ; a, air- 

 chamber ( x 240). 



Since the long axis of the stomata coincides in this instance 

 with the long axis of the leaf, it is easy to obtain correct cross- 

 sections of the stomata. The section should be taken at right 

 angles to the long axis of the leaf. For this purpose a narrow 

 strip, say about J inch long and T \> inch broad, should be cut out 

 of the leaf, in the direction of its length, with a pair of scissors ; 

 this strip can be supported between two pieces of the pith of the 

 elder or of the sunflower, or, though less advantageously, between 

 two pieces of carrot or of fine bottle cork ; or, several such strips 



6 



