257 



resembles tha,t of the upper, but the cells are greatly elongated 

 just above the veins and at that place stomata are wanting. 

 The stomata are placed both upon the upper and lower surface, 

 with their apertures principally in the direction of the length 

 of the leaf. Glandular hairs are absent. 



The mesophyll (Fig. 9) is very loosely arranged. All the cells 

 above the veins are cylindrical — either shorter or longer — with 



Fig. 10. Saxifraga stellaris. 



A, Epidermis of the upper surface of the leaf. B, The same (transverse section). C, 

 Epidermis of the lower surface of the leaf. D, The same (transverse section). (A, B, С 



and D 2-2/j). 



their axes at right angles to the epidermis. They can be readily 

 distinguished from the stellate cells of the spongy parenchyma 

 which form a very large-celled lacunose tissue. How many of 

 the 3 — 4 layers of cylindrical cells are to be called palisade- 

 cells ("collecting-cells" of Haberlandt) is quite arbitrary. 



The veins are accompanied by colourless, one-layered (rarely 

 many-layered) bundle-sheaths. Mechanical tissue is entirely 



