discussion. We may treat these factors under two heads, 

 radiant energy and wind. 



(a) Radiant Energy. The ultimate source of all our energy 

 is the sun. It manifests itself upon the earth as ether vibrations 

 which give rise in our bodies to the sensations of light and heat 

 depending only upon their rate of vibration. With the plant, 

 however, it is simply a difference in energy, not sensation. So 

 closely are these two factors related that it is almost impossible to 

 differentiate their effects. However, light would seem to be the 

 more important, controlling as it does one of the vital processes, 

 photosynthesis. Ascending the mountain the atmosphere becomes 

 rarer, hence the intensity of the light proportionally greater as 

 higher altitudes are reached. Plants able to withstand this 

 greater intensity must possess protective structures. They have 

 become "light loving" species, as expressed by authors. It 

 would seem more pertinent, however, to designate them as light 

 enduring forms. The absence of broad leaved species, the high 

 development of cutinization, and palisade structures may be, in 

 part, responses to this high light intensity. 



Closely related to the function of photosynthesises that of trans- 

 piration or water loss. Both these functions are largely depend- 

 ent upon the stomata for their efficiency, at least in the alpine 

 forms under consideration. The stomata are primarily paths of 

 gaseous exchange, but are also the canals of water loss. The latter 

 necessarily occurs where wet membranes are exposed to an 

 atmosphere of less diffusive tension. The amount of transpira- 

 tion is dependent in part upon the aperture of the stomata, which 

 is in turn dependent upon the light intensity, the temperature of 

 the air and its relative humidity. This transpiration loss is vital 

 in the economy of plant life and especially is this true of alpine 

 regions where the absorption, due to the low temperature of the 

 soil, is at a minimum and the transpiration, on account of the 

 high wind velocity, greatly augmented ; it should be said, how- 

 ever, that some experiments seem to show lessened transpiration 

 in alpine regions. 



In response to these precarious conditions we find protective 

 adaptations which tend to mitigate the harmful effects which 

 might otherwise arise. Whether they have been developed 



