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- 

 Fig. 22. Cassiofe hypnoides. cularized layer, and they 



The leaf. 1, Transverse section. 2, Longitudinal section haVC rOUUdly aUgular 

 not including the middle vein. 3, Stoma. 4, Epidermis 



with stomata. (Greenland. Aug. 1, l&9i2.) (H. E. P.) lateral WallS ; OUly 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- 



