CHAPTER II 

 REGIONS OF VEGETATION 



i. Climatic Factors causing the Differentiation of Regions. Distinctive features 

 and diagnoses of the three regions— basal region, montane region, alpine region. Com- 

 parison between mountain-regions and zones. Former exaggeration of the effects of 

 heat. Humboldt's views. 2. Plant-life in Mountain Regions, i. Mountain-woodland. 

 Mountain-grassland. Mountain-desert. Sequence" of woodland climate, grassland climate, 

 and desert climate with increasing altitude. Identity of the formations in the basal and 

 montane regions with those of the lowlands. Characteristic habit of alpine formations, 

 ii. The Features of Alpine Plants. Alpine habit. Elfin-tree. Shrubs. Cushion-plants. 

 Rosette-plants. Grasses. Xerophilous structure. Colours, dimensions, scent of flowers. 

 Periodic phenomena. Bonnier's and Kerner's experiments on the influence of the mountain 

 climate on the structure of plants. Influence of individual climatic factors. Assimilation 

 and transpiration in alpine regions. Increase of sugar in nectaries. Application of 

 experimental results to the natural alpine vegetation, iii. The Occurrence of Alpine Species 

 of Plants in Lower Regions. Occurrence of tropical alpine plants in lower regions as epi- 

 phytes and in solfataras. Differences between arctic and alpine plant-structure, iv. The 

 Upper Limit of Plant-life in High Mountains. Saussurea tridactyla. 



1. CLIMATIC FACTORS CAUSING THE DIFFERENTIATION 



OF REGIONS. 



On ascending a mountain the first changes in the vegetation that occur 

 are due to the increase in the atmospheric precipitations. Where the vege- 

 tation in the lowlands is poor, it becomes richer on the mountain ; where in 

 the plains the forest occupies only the parts irrigated by the rivers, it extends 

 in more extensive and more coherent masses on the lower mountain slopes. 

 The dominant species of plants, for instance the commonest forest trees, on 

 the mountains are the same as those growing in moist places in the plains ; 

 their mode of life and structure are still unchanged. 



With increasing altitude a second climatic factor influencing vegetation 

 reinforces moisture — the fall in temperature. All those characters of plants 

 that are directly or indirectly dependent on heat are accordingly modified. 

 Species that dwell in the plains in higher latitudes appear and replace those 

 of the adjoining plains, and the latter accordingly diminish in numbers. 

 The general features, systematic as well as oecological, of the vegetation 

 have been changed as if by transference towards the north or south pole. 



At a still greater altitude, the atmospheric precipitations become weaker, 

 whereas the fall in temperature continues. But other factors of the moun- 

 tain climate now make their influence felt on plant-life, such as rarefaction 

 of the air, intense solar and terrestrial radiation, strong winds. Vegetation 



