7i6 ZONES AND REGIONS [Pt. Ill, Sect. IV 



considering the shortness of the growing season, evergreen foliage appears to 

 be very suitable ; but what are the influences which determined the adop- 

 tion of this habit in types that, like willows, are deciduous elsewhere, is still 

 unknown. Also the earlier development of the flowers in comparison 

 with the lowlands is physiologically unexplained. Many phenomena are 

 even oecologically enigmatic, for instance the cushion-growth, which is 

 obviously an adaptation to the alpine climate, and the characteristic habit 

 of the elfin-wood. Both cases are most probably connected with the 

 violent winds. Strong wind is the sole feature common to the habitats 

 of the cushion-plants on the islands in southern seas and in the alpine 

 region, and the elfin-tree form is repeated frequently in trees and shrubs 

 standing alone on open windy sea-coasts. 



iii. THE OCCURRENCE OF ALPINE SPECIES OF PLANTS IN 

 LOWER REGIONS. 



The flora of the alpine region is composed everywhere of species which 

 either (a) belong exclusively to it, or (b) occur also in lower mountain 

 regions and in the lowlands. Plants belonging to the second category are 

 particularly interesting, as their occurrence in different habitats throws 

 much light on conditions of existence in the alpine climate, and confirms 

 the views already arrived at. 



Species from the grassy tracts of the lowlands, that occur on alpine 

 meadow and mountain steppe, appear to be so modified, that they are 

 frequently distinguished as varieties — var. alpina. Such alpine forms possess 

 peculiarities that we have learned to recognize as the direct effects of the 

 mountain climate. 



Alpine plants that occur in the moist basal and montane regions betray 

 by their habitats their marked xerophilous character. Thus, a number of 

 Javanese alpine plants occur in the lower rainy regions, but there either 

 as epiphytes, for instance Rhododendron javanicum, R. retusum, Vaccinium 

 polyanthum, or as plants of the saline soil of solfataras 1 . In Japan, Mayr 

 has also observed a rich vegetation of alpine plants in the solfataras of 

 lower regions. For the same reasons many alpine species from the Atlas 

 Mountains occur in Algiers on the sea-shore, but not in intervening 

 regions 2 . 



In the above-mentioned cases, the analogy in the conditions of existence 

 at the different stations consists in the impeded water-supply, risk from which 

 is guarded against by the possession of xerophilous characters. Tempera- 

 ture does not enter into the question. On the other hand, temperature 

 is a factor, with those inducing xerophily, determining the occurrence 

 of many lowland plants of higher latitudes on high mountains of lower 



1 See p. 386. 2 See Battandier, op. cit. 



