50 



A MONTANE BAIN-FOEEST. 



Ravine. A graph of temperature was secured in the midst of a heavy- 

 mass of hepatics and mosses which was serving as the substratum of 

 a nmnber of epiphytic orchids, 10 feet from the ground on a Windward 

 Slope. This epiphytic substratum showed a less daily range of tem- 

 perature than the air of the same situation during the same week 

 (6.4° F. as against 9.4° F.), and, as compared with the soil in the Wind- 

 ward Ravine, it exhibited the same minimum and a higher maximum 

 temperature. The mean daily range of soil temperature is so slight in all 

 cases as to be without significance. It is less than 2° F. in all habitats 

 excepting the Ruinate, and is only 1.1° F. in the Windward Ravines. 

 The investigation of the daily march of soil temperature was under- 

 taken partly with a view to investigating the possible relation of the 

 daily march of soil temperature to the activity of hydathodes. The daily 



Table 12. — Recapitulation of soil-temperatwe data for different habitats. 



range of temperature was found to be so slight and the lag of the daily 

 minimum to be so short that there is no warrant for considering the soil 

 temperature to be of importance in the operation of these structures. 

 Differences of as much as 10° F., such as exist between the forested 

 soils of the Windward Ravines and the open slopes of the leeward side 

 of the Blue Mountains, are great enough to play a slight role in the 

 distribution of plants, and this difference is perhaps partly responsible 

 for the occurrence of lowland species at higher elevations on the leeward 

 than on the windward side. Aside from this greatest difference in 

 soU temperature, the factor is of no importance in the differentiation 

 of habitats nor in the explanation of plant activities, and its measure- 

 ment is of relatively little value in this region. 



