380 



subepidermal layer of the lower surface and the rest of the 

 mesophyll. 



In Fig. 21, A the ep i them a of the leaf-apex is shown; 

 it is peculiar owing to the highly undulating cell-walls. The 

 water-pores occur upon the slanting, upturned terminal sur- 

 face (Fig. 21, B). 



I found no essential differences in leaves from the different 

 regions. It is an interesting fact which is pointed out by 

 BôRGESEN, namely that the structure of the leaf becomes looser 

 with increase of the geographical latitude (Dovre— Kaafjord 

 (70° IN. lat.) — Nova Zembla). 



The leaf- s talk is reniform in transverse section. There 

 are three vascular bundles and a large central lacuna. 



R. pygmæus Wahleul). 



Lit. BccHENAU & FocKE, 1872, p. 28. Lange, 1880, p. 55; 

 1887, p. 254. Nathorst, 1884, p. 46, tab. 1. Lindman, 1887. 

 pp. 25, 41, 100, tab. 1, fig. 7 A. B. Rosenvinge, 1892, p. 675. 

 Wagner, 1892, pp. 8, 20. Hartz, 1894, p. 52; 1895, II, p. 288. 

 Børgesen, 1895, pp. 255, 236. Norman, 1895, p. 11. Ekstam, 1897, 

 p. 145. Abromeit, 1899, p. 30. Ekstam, 1899, pp. 22, 32, 37. 

 Restoll, 1900, figs. 11, 26. Andersson & Hesselmann, 1901, p. 48. 

 Gleve, a., 1901, pp. 51, 78, 88, 103. Ddsén, 1901, p. 30. Frei- 

 denfelt, 1904, p. 53. Sylvén, .1906, p. 272. 



Alcohol material from Greenland (Danmarks 0, Aug. 1891 ; 

 Godhavn in Disco, 20. 7. 1884; Kutdlisat in Disco, 9. 8. 1890 [var. 

 Langeana]] Norge (Trondfjældet Jemtland, 19. 6. 1880); Spitz- 

 bergen (Advent Bay, 3.8. 1810; Middelhook in Belsund, 1. 7. 1882). 



B.pygmæus is a perennial herb. The rhizome is vertical; 

 roots arise from the whole of its surface and it is covered 

 with a dense matting of the vascular strands of dead leaves. 

 Though the rhizome does not become long yet some are com- 

 monly found measuring as much as 2 cm. in length. The plant 

 often grows in dense tufts which are produced by the rhizomes 

 branching freely and the individual shoots readily become de- 



