26 



Knud Jessen. 



Fig. 9, A shows that the leaf-margins may be revolute, 

 which is especially the case in /. humilis; and the tomentose 

 hair-covering of the lower surface is a good protection for the 

 leaf against the danger of excessive transpiration. Both 



Fig. 9. Potentilla pulchella. 



A, Transverse section of a leaf-segment. B, Fragment of a transverse section of 

 a leaf of /. elatior, tiie inner wall of the upper epidermis is highly mucilagi- 

 nous. C, Stoma from the lower surface of the leaf. Z), Epidermis of the 

 upper and E of the lower surface of the leaf ; h, the base of a hair. F, 

 Section of spongy parenchyma parallel to the surface. G, Fragment of 

 transverse section of rhizome ; c, cambium ; m, pith ; p, periderm ; r, medul- 

 lary rays. X xylem. A, From Tempel Bay in Spitzbergen: J5, C, D, E, F 

 and G from Snenæs in Greenland (A and G about i^/i ; B, C, D, E and F »»/i). 



leaf-surfaces have scattered glandular hairs. Upon the upper 

 surface only a few stomata occur which are situated on a 

 level with the leaf-surface; the numerous stomata upon the 

 lower surface are on the other hand usually slightly projecting 



