714 



ZONES AND REGIONS [Pt. I IT, Sect. IV 



The phenomena that have been proved to exist by Bonnier and Kerncr can 

 all be traced back to well-known factors of the mountain climate. 



Mountain light owing to its greater intensity has a stronger retarding 

 action on the growth of axes and leaves than has light in lowland. The 

 great intensity of light also causes the stronger development of certain 

 pigments, especially of anthocyan, in flowers and foliage, whilst on the 

 other hand it causes a more rapid decomposition of the chlorophyll. The 

 richness of mountain light in ultra-violet rays probably favours the develop- 

 ment of flowers. 



The desiccating action of the mountain climate caused by the strong 



Fig. 416. Tencrium Scorodonia. Leaf in 

 transverse section. a in mountain 

 climate, b in lowlands. After Bonnier. 



Fig. 417. Galeopsis Tetrahit. Leaf in 

 transverse section. a in mountain 

 climate, b in lowlands. After Bonnier. 



insolation, the rarefaction, and the movement of the air, partly acts in 

 the same direction as does the intense light with regard to the production 

 and growth of vegetative shoots and flowers. But in particular it causes the 

 xerophilous structure of the foliaged parts that occurs in all alpine plants, 

 and the strong development of the roots likewise common in xerophytes. 



The lotv temperature, especially at night, retards the nocturnal growth 

 in length. The coldness of the winter also causes plants of very wet 

 habitats to retain their xerophilous structure. 



The effects of the mountain climate on various metabolic processes are less clear. 

 Bonnier has compared plants from his alpine cultures in sub-alpine stations with 

 those grown in the latter, as regards their assimilation of carbon, their respiration, 

 and their transpiration. The results were that equal surfaces of alpine individuals 



