114 



THE PHYSIOLOGY OF PLANTS 



ni, 



glandular protuberances on the under surface o£ the leaf. 

 These are formed by the tubular elongation of cells (int), 

 which in their normal condition have the appearance shown 

 in m, and are therefore provided with considerable intercellular 

 spaces. The diseased tissues on the under side of the leaf 

 become more like the normal pallisade parenchyma (p) of the 



riG. 17.— Tbansversb Section THEonoH thb Leaf of Fims elastiea sufpeking 



FKOM OVHK-WATBKING. 



upper surface of the leaf, which is covered in by a triple 

 epidermis (E). Of these three layers, the outer one consists 

 of very small cells, which are, however, covered in by a very 

 thick waxy cuticle. The innermost layer of the epidermis 

 is formed by thin-walled comparatively large cells (w), which 



