392 



shows a leaf transitional between the two types ; the mesophyll 

 of the upper surface is pahsade-Mke, and there are three bundles. 

 The bundles are without stereom, but have a more or less 

 distinct sheath containing chlorophyll. 



Each leaf-apex has an e pi the ma which opens at the 

 margin (Fig. 35, G). The cells have highly undulating walls, 

 similar on the whole to those in B. nivalis. 



R. liyx)erboreus ßottb. 



Lit. Hooker, 1833. Lindman, 1887, p. 41, fig. 8 a, b, tab. I. 

 Hartz, 1894, pp. 6, 34; 1895, (11), p. 289. Norman, 1895, p. 8. Rosen- 

 viNGE, I, 1892, p. 675; III, 1896, p. 108. Krüdse, 1897, p. 385. 

 Abromeit, 1899, p. 30. Andersson & Hesselman, 1900, p. 47. 

 Resvoll, 1900, fig.-., 4, 5, 13, 20, 22, 23, 25, 27, 28, 30, 33. 

 Düsen, 1901, p. 30. Porsild, 1902, pp. 170, 196, 205. Simmons, 

 1906, p. 115. 



Alcohol material from Greenland (Friedrichsthal, 29.8. 1883, 

 Jacobshavn, 26.7.1884, Sermilik, 3.7.1885, Kingigtortadlit, 

 1.7. 1887, Uperniviarsuk, 9.7. 1887, Niodluisuk-0en, 21.8. 1888). 

 Iceland (Thingvellir, 13. 6. 1895). Lapmark (Bosekob, 3. 7. 1884). 

 Spitzbergen (Gåseoen 28.7.1882). 



R. Jnjperboreus bears a great resemblance to B. lapponicus 

 but is distinguished from the latter inter alia by the form of 

 its leaf, by its more abundant branching, and by its much 

 shorter flower-stalks. The leaf is deeply tripartite, the lobes 

 are narrower than in R. lapponicus^ the middle one is entire 

 and the lateral lobes are often shallowly 2-lobed (Fig. 36). The 

 leaves are placed in two rows upon the slender stem the inter- 

 nodes of which are curved. The internodes may reach a length 

 of 10 cm. Usually every leaf subtends a lateral shoot which 

 is antidromous to the main axis. The first leaf of the shoot 

 is situated dorsally and somewhat sideways, and its internode 

 is elongated. It is no doubt usual for 3 — 4 generations of axes 

 to attain the flowering-stage during the same year; the first 



