124 THE LIFE OF THE PLANT 



kinds of cells : in the upper part of the leaf the cells 

 are cylindrical in shape and arranged like stakes in a 

 palisade, vertical to the surface of the leaf. In the rest 

 of the leaf the cells are of varied and irregular form, 

 with considerable spaces between them. All the cells 

 of the ground tissue, especially those of the palisade 

 layer, contain minute green granules ; we shall return 



FIG. 35- 



to them presently, only noting here by the way that the 

 leaf, like all green parts, is in itself colourless, and owes 

 its colour to those granules. The epidermis which we 

 see here in surface view and in section consists of flat, 

 oblong, almost tabular cells. Between them on the 

 lower surface of the leaf there are scattered organs of a 

 special form one of them happens to be cut in half at the 

 edge of the section. We notice that it consists of two cells, 

 each curved into an arch, forming between them an oblong 

 slit. These are apertures, like ventilators, in the lower 



