CLIMATE AND PLANT GROWTH. 3 



tions of comparable or " standard " plants developed under the par- 

 ticular climatic conditions summarized, are essential steps in a 

 successful investigation 



THE EXPERIMENTS. 



The investigations here reported were conducted in the vicinity 

 of the Great Basin Forest Experiment Station, located on that part 

 of the Wasatch Mountains embraced by the Manti National Forest in 

 central Utah. Here, from the foothills to the highest elevations, be- 

 tween altitudes of approximately 7,000 and 11,000 feet, three distinct 

 plant associations (identical in this locality with vegetative types or 

 life zones) occur. In the heart of each of these associations a type 

 station was selected in 1913. From 1913 to 1916 the more important 

 environmental factors were recorded, and, accordingly, the climatic 

 characteristics of each type-zone are well known. The investigation 

 of the influence of the weather upon the development of comparable 

 plants, with which the present paper is chiefly concerned, was begun 

 in 1915 and continued and extended in 1916. The types here recog- 

 nized and their approximate altitudinal limits are as follows: 



Sagebrush-rabbit-brush association feet 5, 200- 6, 500 



Oak-brush association do 6, 500- 7, 800 



Aspen-fir association do 7, 500- 9, 500 



Spruce-fir association __ __do 9,000-11,000 



As indicated by the plants typifying the respective associations, all 

 but the lowest are forested. No special investigations were con- 

 ducted in the treeless type. 



The meteorological stations are located at elevations of 7,100, 

 8,700, and 10,000 feet. They are all in the same canyon, and the 

 distance between the lowest and the highest stations in an air line 

 is approximately 5 miles. Owing to the possibility of the results 

 being influenced by the presence of trees and other objects in the 

 vicinity of the physical instruments and growing plants, the stations 

 are all located in the open, on slopes dipping slightly to the south, 

 and no vegetation is so close as to cast shadows on the instruments or 

 potometers, except for a few minutes at sunrise and sunset. Also, 

 the instruments and plants are placed as near together as practicable 

 (each type station covering one twenty-fifth of an acre), so that the 

 conditions recorded may be practically identical with those acting 

 upon the plants. 



The investigations have been concerned chiefly with ( 1 ) recording 

 and summarizing the meteorological data, and (2) determining the 

 relation of certain potent weather factors to growth, water require- 

 ment, and certain other physiological functions of standard plants 

 developed under different climatic conditions. Measurements of 



