147 
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 leaf. 
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 Ill. 
Chloroplastids occur in both the upper and lower epidermis 
(cf. Livrorss). The mesophyll consists of a well-marked pali- 
sade-tissue, formed by 2—8 layers of cells of no great height, 
10* 
