216 OXYLOPHYTES SECT, vi 



Cembra, iorm the same type of scrub. Betula pubescens, possibly repre- 

 sented by the sub-species B. pubescens carpathica, grows on lichen-heath 

 and high-moor in Lapland : the individuals are often isolated, and are 

 closely applied to the ground as deformed individuals, which require fifty 

 to sixty years for the stem to attain a length of 2 metres and a thickness 

 of 4 centimetres, and possess branches that do not rise above the general 

 surface of the lichen-heath. But in more favourable spots the plant is 

 taller and forms scrub, which is about 1-2 metres in height and may 

 entertain large-leaved, mesophilous, perennial herbs. The birch oecologi- 

 cally approaches species that are xerophytic in structure ; like the 

 conifers it attaches itself firmly to bare, sun-heated sandstone rocks of 

 Saxon Switzerland ; it also produces bushland and forest above the 

 coniferous belt in northern Europe. Its ' lacquered ' leaves obviously 

 provide protection against transpiration. 



At high altitudes forest does not suddenly cease ; it dwindles to form 

 scrub composed of short trees and shrubs, below the level of the open 

 grassland and fell-field, which consist of herbs, lichens, mosses, and 

 dwarf-shrubs. This scrub is composed of different species in different 

 parts of the Earth. In high alpine situations elfin-scrub is the most 

 widely known xerophytic bushland. 1 It is formed by varieties of Pinus 

 montana (var. Pumilio, var. uncinata, and var. Mughus), which in more 

 western places (Western Alps and Pyrenees) become tall trees and appear 

 between the limit of forest and the alpine grassland. An erect stem 

 is not developed ; the stems creep over the ground, descend slopes, are 

 clothed with mosses and other plants, strike root, and send up bow-like 

 strong branches ; these last may exceed man's height, and are packed 

 together often so tightly and firmly as almost to form cushions that can 

 bear the heaviest loads of snow. Whole mountain slopes or ridges may 

 be clothed with dark green, interlacing masses of elfin-wood so densely 

 as to be impenetrable, or often more easily passed over than passed 

 through. The soft, humus-laden, often completely peat-like, soil absorbs 

 much water. Screened from wind by the crowns of the elfin-wood bushes, 

 there develop a number of plants which blossom earlier than those on 

 the adjoining rocks and alpine grassland, and which vary in nature 

 according to the amount of light, the number of fallen coniferous needles, 

 and the like. In younger communities there are rhododendrons, juniper, 

 roses, Daphne, Polygala Chamaebuxus, Empetrum, species of Vaccinium, 

 Erica carnea, Calluna, and other low xerophilous shrubs, also many species 

 of Prunella, Digitalis, and Campanula, many grasses and sedges, as well 

 as mosses and lichens. This elfin-scrub is a xerophytic type of vegetation 

 which is well able to withstand, on the one hand, rapid transpiration, 

 intense sunlight, and cutting cold winds, and, on the other hand, the 

 exceeding moisture of a wet soil, frequent and dense mists, falls of rain 

 and of snow. The elfin-tree and ling are two parallel and readily satisfied 

 species, which are easily driven out by other species to places where the 

 conditions of life are most unfavourable. This alpine scrub, composed 

 of Pinus montana, on peat soil is allied to dwarf -shrub heath. The bog- 

 pine, Pinus montana var. uncinata, is a characteristic tree in the high- 

 moor of Switzerland, according to Schroter ; 2 sometimes it spreads 



1 Kerner, 1863; Friih und Schroter, 1904; C. Schroter, 1904-8; Hayek, 

 1907- * Schroter, 1904. 



