INVERSIONS OF TEMPERATURE. 47 



illustrated in the region of the Coconino forest bordering upon 

 the famous Grand Canon of the Colorado River in northern 

 Arizona, where many moisture-loving species may be found 

 fringing the rim of the canon, which are not to be seen in such 

 abundance elsewhere on the mesa. Razoumofskya robusta vagi- 

 nata (Willd.) Kuntze is a loranthaceous parasite growing on 

 the branches of the bull pine (Pinus ponderosa var. scopuloruni) 

 throughout the transition zone. It is most abundant, however, 

 along the margins of mesas, the rims of canons, and hilltops, 

 and reaches its greatest density along the Grand Canon on the 

 Colorado River. Here the heated air, rising from the river 

 under the influence of the subtropical sun, loses about 20 F. in 

 its ascent of 2000 meters, and as a consequence it pours over 

 the mesa much cooler and with its relative humidity increased 

 to near the point of saturation. The Razoumofskya finds this 

 strip of territory, where the effect of the moist air is greatest, 

 most advantageous in the germination of its seeds and the 

 attachment of the seedlings to the host plant. It is therefore 

 most abundant in a belt one or two kilometers in width, run- 

 ning parallel to the rim of the canon, while it is comparatively 

 infrequent at greater distances. Within this belt it is estimated 

 to have gained a foothold on more than half of the pine trees. 



In conclusion, I must again remind you that none of the 

 meteorological principles described are in any sense original 

 with myself ; but I am able to adduce some very striking ob- 

 servations in illustration of their influence upon vegetation, 

 and it is confidently believed that this work constitutes the 

 first systematic attempt to use such data in explanation of cer- 

 tain seeming aberrations of distribution and zonal boundaries. 

 Furthermore, it is most interesting to note that the effects of 

 cold-air drainage and inversions of temperature have been taken 

 into consideration by the horticulturist and farmer long before 

 this analysis of their relations to the facts of natural distribu- 

 tion of plants and animals was brought forward. 



