Rosaceæ. 69 



the leaves are torn off or extremely small, and linear with involute 



Kill-edges; the leaves to the leeward of the shrub are larger 

 and their leaf-edges are involute in a less degree or not at all." 

 Hartz gives in the same place some information regarding 

 the habitats of the different forms in East Greenland. Thus 

 he found D. octopetala agenuina, which has large broad leaves, 

 in damper localities in sheltered spots, and it was covered with 

 -now dining winter, while ß minor, which had small narrow 

 leaves, y hirsuta, à argentea and D. integrifolia were found 

 in dry localities, and were usually not snow-covered during 

 winter. The young leaves which live through the winter 

 are so highly revolute that I ho lower surface is almost entirely 

 covered. Warming remarks in his notes that the leaves 

 when dry roll back towards the condition of the bud-stage, 

 but on getting wetted they spread out again. As the stomata 

 only occur on the h »wer surface the importance of the revolute 

 condition is easily understood. 



The epidermis of the upper surface has a very strong 

 outer wall which is somewhat thicker in the winter leaves 

 than in those of the summer. Thus in the latter it was found 

 to be 2.5// (Iceland and Copenhagen I, 4 .4 p. (the most common i 

 and 6 p (D. octopetala from downs at Dove Bay in N. E. Green- 

 land) and m the winter leaves 6 — 7 p (D. octopetala from Dan- 

 marks off East Greenland) and 8 p. (Iceland). The cuticle 

 is considerable; it is smooth and the cutinized portion con- 

 stitutes above one-half of the wall; its inner limit is distinctly 

 toothed (Fig. 27, B). Kruch (1. c.) records that in D. octopetala 

 Mir walls of the upper epidermis are mucilaginous; this I also 

 have found to be the case, though not in all the cells; on the 

 ut her hand, he denies the presence of mucilage in D. integrifolia, 

 but this difference I have not been able to verify (cf. Fig. 27, B). 

 The palisade parenchyma is very thick ami is composed (if 

 about three layers of cells. The spongy parenchyma is rather 

 loose and consists of slightly branching cells (Fig. 27, D). 



