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- 

 ih'ss of the outer wall in the upper epidermis about 3//, 



Fig. 30. Rubus saxatilis. 



.1, Transverse section of leaf. />', Epidermis of the upper surface of the leaf. ('. 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- 

 dcrmis; />, outermost layer of the pericycle. A, B, C, D from Greenland, K from Denmark 

 (.1. C, D, E M %; B »%). 



in lower epidermis about 2//, the corresponding dimensions 

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

 land) were : 130 //, about 4.4// and about 3.3//. An 

 explanation of these differences is suggested by 1 he vague 



