56 REPORTS ON INVESTIGATIONS AND PROJECTS. 



in harmony with resuUs secured with the giant cactus by similar methods, 

 and seems to point to an increasingly unfavorable incidence of the rainfall 

 of the germinating season, without regard to its amount. 



Vegetation in the Santa Catalina Mountains, by Dr. Forrest Shreve. 



The work which has been under way for several years on the climate and 

 vegetation of the Santa Catalina Mountains has been actively prosecuted 

 during the past summer and brought to a close. The instrumentation has 

 been made more complete than in previous years. Records of rainfall have 

 been secured at six stations separated by vertical intervals of i,ooo feet, and 

 at each of these stations a record of evaporation-rate for the growing season 

 has been secured for both southern and northern exposures. Hygrographs 

 were operated at 4,000 and 7,000 feet altitude, and a daily record of maxi- 

 mum and minimum temperatures at 8,000 feet was secured through the 

 cooperation of Mr. J. G. Brown. Determinations of soil moisture for north- 

 ern and southern slopes at the six stations were also made at critical times in 

 the growing season. The conditions of atmospheric and soil aridity prevail- 

 ing in the desert during the dry foresummer have been found to extend, with 

 far less amelioration than was supposed, to the heavily forested altitudes; 

 the midsummer rainy period, however, being one of great differentiation at 

 the several elevations. 



Data are now in hand to work out a number of features of correlation 

 between the distribution of vegetation and that of the chief environmental 

 factors. 



Climatic Control of Groivth Activities, by Dr. Forrest Shreve. 



Field work has been carried on with a view to determining the growth- 

 rate and establishment-rate of the Arizona yellow pine (Pinus arisonica) at 

 four elevations, 1,000 vertical feet apart, within its natural range in the 

 Santa Catalina Mountains. Observations have been made on areas of i hec- 

 tare in typical localities with southern exposure, and have been taken so as 

 to show total population, diameter of all individuals, height of individuals 

 less than 3 meters high, and the age of selected individuals of all ages, as 

 determined by ring count. These data make it possible to determine the 

 curve of average growth-rate for the pine at different ages, and its curve of 

 average growth-rate during the past 100 years. These two curves, secured 

 for each of the several altitudes, show graphically the greater activity at the 

 higher elevations, in both growth and establishment. When these data are 

 viewed together with those on the climate of the Santa Catalina Mountains, 

 they form an addition to our knowledge of the correlation between distribu- 

 tion of climatic conditions and the activities of the same species under these 

 distinct conditions. 



