964 The Trees of Great Britain and Ireland 



This variety, which was long considered to be a distinct species, has been 

 shown by Beissner and Schneider to be an abnormal form of B. pubescens. It 

 differs from the type in the longer, more acuminate, slightly lobed leaves ; and in 

 the fruiting-catkins, which are very long {\\ inch or more) and slender, with 

 pubescent ciliate scales, the middle lobe of which is elongated. The leaves and 

 fruit are shown in Plate 269, Fig. 2. 



This peculiar form has been found wild in the province of Wermland, in Sweden, 

 and is only a tree of small dimensions. It is often planted in botanical gardens. 



5. Some peculiar forms have arisen in cultivation, as var. aurea, young foliage 

 tinted with yellow, sent out a few years ago by G. Paul, Cheshunt Nurseries ; and 

 var. nana, a dwarf form. 



Hybrids 



1. Hybrids have often been observed between this species and B. verrucosa, 

 and have received various names, as B. hybrlda, Bechstein, in Diana, i. 80 (1797); 

 B. aurata, Borkhausen, Forstbot. i. 498 (1800); B. glutinosa, Wallroth, Sched. Crit. 

 497 (1822); and B. ambigua, Hampe, in Reichenbach, Fl. Sax. 120 (1842). These 

 hybrids are intermediate in the characters of the branchlets, foliage, and fruit ; and 

 may be suspected in cases where the branchlets are more, or less glandular and 

 show slight pubescence. 



2. B. intermedia, Thomas, in Gaudichaud, FL Helvet. vi. 176 (1830), a hybrid 

 between B. pubescens and B. nana, is a shrub about 10 feet high, with small 

 leaves, which is found in the Swiss Jura, Greenland, Iceland, northern Europe, 

 and Siberia. This has been collected^ in a few localities in the Highlands of 

 Scotland. 



Distribution 



This species is widely distributed through Europe and northern Asia, extend- 

 ing farther northward than B. verrucosa, but not descending so far south. It is the 

 most northerly tree in Europe, growing on the shores of the Arctic Sea from North 

 Cape (lat. 71°) to the mouth of the White Sea; its northern limit eastward 

 through north-eastern Russia and Siberia to Kamtschatka being near the 

 Arctic circle, though in some localities it ascends a degree or two higher. Its 

 southern limit in Russia and Siberia appears to be the edge of the steppes, on 

 which the tree does not grow ; but it occurs in the Caucasus and Armenia. Farther 

 westward the southern limit is the Carpathians and the Alps ; and the tree is not 

 found in the Apennines or in the Pyrenees, its most southerly point in France being 

 near Grenoble. It is also a native of Iceland and of south-western Greenland. 

 The distribution may then be roughly described as the northern hemisphere, 

 from Greenland in the west to Kamtschatka in the east, between the parallels 

 of 45° and 71°. 



As compared with B. verrucosa, this species is found on the continent of Europe 

 on wetter soils and in moister climates, and is the birch which grows on marshy 

 ground and on undrained peat-mosses. 



' Cf. E. S. Marshall, vajourn. Bot. xxxix. 271 (1901), and Bot. Exchange Club Report for 1904, p. 33. 



