106 
which has neither furrows nor hollows. The leaf is shortly 
acicular, without protective devices except its small size. In 
agreement with the statement above given under Cassiope tetra- 
gona, the intercellu- 
lar spaces are rather 
limited in size. But 
I am not prepared to 
say whether this is 
caused directly by the 
fact of the leaves hav- 
ing such slight external 
protective devices, or 
whether the chief rea- 
son must rather be 
found in the smallness 
of the leaf, which does 
not allow superabun- 
dant internal space. 
The upper and 
lowerepidermis are very 
much thickened by the 
presence of a cuticle 
and beneath it a cuti- 
cularized layer, and they 
Fig. 22. Cassiope hypnoides. 
The leaf. 7, Transverse section. 2, Longitudinal section have roundly angular 
not including the middle vein. 3, Stoma. 4, Epidermis f 
with stomata. (Greenland, Aug.1, 1892.) (H.E.P.) lateral walls , only a 
few unicellular hairs of 
no importance occur along the margin of the leaf; the latter is 
usually somewhat flattened. The stomata, which are not confined 
to any particular area, project slightly or else occur on the level 
of the epidermis. The cells of the outer layer of the mesophyll, 
and partly those of the layer beneath are developed as palisade- 
cells and slant towards the apex when seen in longitudinal section. 
The central mesophyll has no large intercellular spaces and con- 
