Rosaceæ. 



79 



one summer only, and is moreover strongly influenced by 

 light The leaves from Greenland (Tasermiut-Fjord) had 

 the following dimensions: Thickness of leaf 110 //, thick- 

 ness of the outer wall in the upper epidermis about 3/^, 



Fig. 30. Rubus saxatilis. 



A, Transverse section of leaf. B, Epidermis of the upper surface of the leaf. C, Epidermis 

 of the lower surface of of the leaf. D Section of the spongy parenchyma of the[leaf parallel 

 to the surface. E, Fragment of an absorbent root of second order ; c, the cortex, the radial 

 and outer tangential walls of its innermost layer have highly thickened walls ; end, endo- 

 dermis ; p, outermost layer of the pericycle. A, B, C, D from Greenland, E from Denmark 

 (A, C, D, E 280/,; В "»/,). 



in lower epidermis about 2^, the corresponding dimensions 

 from leaves collected in Iceland (Aöalvik in N. W. Ice- 

 land) were : 130 ju, about i . 4: /л and about 3 . 3 /i. An 

 explanation of these differences is suggested by the vague 



