68 



Knud Jessen. 



octopetala y, hirsuta Hartz and å, argentea A Blytt, in the 

 latter the upper surface is densely woolly, and Dryas integri- 

 folia var. canescens Simm., in which the upper surface is 

 densely tomentose. The leaves are revolute in the bud- 

 condition and also as a rule, to a greater or less degree, when 

 full-grown, especially in D. integrifolia (Fig. 27, A ). In this 

 respect it is of importance whether the plant grows in favour- 



£ 



D ~ 



Fig. 27. 



Dryas integrifolia. A, Transverse section of leaf; 20 /i (Eug. Warming, 1887). B, Frag- 

 ment of transverse section of leaf 220 /i)- C, Surface view of epidermis of the upper surface 

 ( 140 /i). D, Section of the spongy parenchyma of the leaf ( 1,0 /i). — Dryas octopetala. E. Hairs 

 from the bundles on the upper surface of the leaf; a, glandular hair ( zw i\); b, branched 



hair ( 50 /,). 



able or unfavourable localities. Thus the most revolute leaves 

 are met with in dry rocky flats or on downs (Dove Bay in 

 N. E. Greenland). Even in one and the same tuft there 

 may be differences as regards the degree to which the leaf 

 is revolute. Hartz (I.e. 1895 a, p. 311) figures a tuft of D. 

 octopetala ß minor from East Greenland, and writes regarding it 

 that "to windward the branches are stunted and decorticated, 



