14' 



The lateral walls are wavy, and thickened to a great extent 

 and irregularly; in transverse section the thinner areas show 

 up sharply against the band-like thickenings. The inner walls 

 do not contain lignin as in Andromeda. Hairs are absent. 



Stomata occur only on the lower surface; they are ar- 

 ranged more or less across the longitudinal axis of the leal. 

 The inner sides of the guard-cells, as well as the neighbouring 



Fig. 4. Diapensia lapponica. 



The leaf. A, transverse section; B, spongy parenchyma seen in surface 

 view; C, stomata. (Greenland) (H. E. P.) 



cells of the mesophyll, are covered by a thin cuticle the 

 presence of which is demonstrated by chlor-zinc-iodine, or by 

 Sudan 111. 



Ghloroplastids occur in both the upper and lower epidermis 

 (cf. LiDFORss). The mesophyll consists of a well-marked pali- 

 sade-tissue, formed by 2—3 layers of cells of no great height, 



10* 



