108 
in all Andromeda-forms is more useful in that respect. Sto- 
mata occur only on the lower surface; they often project 
slightly. The inner sides of the guard-cells, as also the neigh- 
bouring cells of the epidermis are covered by cuticle. According 
to Livrorss chlorophyll grains occur in the upper epidermis. 
Palisade-cells occur in 2—3 layers about 30—40 yw in height 
Fig. 23. Andromeda polifolia. 
The leaf. 6, shews the aqueous tissue and the thick-walled cells beneath the 
vascular bundle in the middle of the leaf. (1—4, Greenland: Tiningnertok, 62° 204. 
5, Denmark: Sjælland.) (H.E.P.) 
at the most, and slanting towards the apex. The spongy 
parenchyma is of about the same thickness as is the palisade- 
tissue and consists of non-branching cells which are usually 
transversely elongated across the leaf, making the latter some- 
what isolateral, which circumstance harmonizes with the often 
somewhat erect position of the leaves. All the cells of the 
mesophyll are somewhat thick-walled. Tannin occurs abundantly 
