52 



Knud Jessen. 



which occurs especially in dry localities, both surfaces of the 

 leaf are white with silky hairs, in the typical form this is 

 the case only on the lower surface, and in the Arctic and Sub- 

 arctic var. Egedii Torr, and Gr. and var. grønlandica Tratt. 

 the leaves are entirely glabrous or somewhat hairy, on the 

 lower surface only, respectively. Fig. 21, D shows a stalked 



Fig. 21. Potentilla anserina (Greenland). 



A, Trausverse section of leaf. B, Surface view of the upper epidermis of 

 the leaf. C, Surface view of the lower epidermis of the leaf ; h, a hair- 

 hearing cell. D, Stalked gland from the lower surface of the leaf. E, Sur- 

 face view of spongy parenchyma. F, Transverse section of an almost ripe 

 pistil ; sm, the seed cavity ; y, outer layer of the fruit-wall ; ae, floating 

 tissue ; sc, sclerenchyma (A, C, D, E about •* i ; B about «/i ; F about w 1). 



gland; such occur scattered along the bundles and are more 

 common on the lower surface. 



The anatomical structure of the leaf, which only lives 

 through one summer, is mesomorphic. The outer wall in 

 the epidermis of the upper surface is about 2.5^ thick; the 

 radial walls are straight or almost straight (Fig. 21, B), but 

 in that of the lower surface somewhat undulating (Fig. 21, C). 



