Vegetation and Altitude. 



63 



Ephedra are of more or less common occurrence in the vicinity, 

 but the fungus has been observed only upon E. trifurca. 

 New Mexico Agricultural College. 



VEGETATION AND ALTITUDE * 



By Charles H. Shaw. 



It has been widely held that the more intense light of 

 higher altitudes exercises a distinct influence upon the vegeta- 

 tion, and a number of considerations support the view. The 

 stunted forms of alpine plants harmonize well with some of the 

 known effects of light, likewise the greater relative develop- 

 ment of their flowers. Bonnier, in his classic experiments in 

 the Alps and Pyrenees, came to the conclusion that light is an 

 important factor in inducing the peculiarities of plants grown 

 at high altitudes. No really discriminating experiments have 

 been made, but the idea has been indorsed by Schimper, Schroe- 

 ter and most of those who have had occasion to refer to the 

 subject. 



Digressing for a time to the general question of light, as 

 an ecological factor, we are impressed by the difficulty of obtain- 

 ing information in this direction. Looking upon light as a 

 form of radiant energy, several workers have attempted to 

 calculate its intensity from astronomical data. Such efforts do 

 not seem to have been happy in escaping fundamental error. 

 For, in making calculations from the sun's altitude, there is not 

 one varying factor, but three or four which must be taken into 

 consideration, viz. : 



Variation according to sine of angle of incidence. 



Disproportionate variation of diffuse light (diffuse light be- 

 ing, probably, a very important factor for vegetation). 



Diminution with decreasing elevation of sun due to increas- 

 ing length of path of light through the atmosphere. 



Disproportionate absorption in lower layers of atmosphere. 



Moreover, there are local conditions quite beyond calcula- 

 tion. Wiesner has given heavy blows to the idea that theoreti- 

 cal calculations are of any real value at all. His readings in 



* Abstract from paper read before the Botanical Society of America at the Baltimore 

 meeting, December, 1908. * 



