ECOLOGY. 341 



ECOLOGY. 



Clements, F. E., Tucson, Arizona. Associate in Ecology. (For previous 

 reports see Year Books Nos. 16-18.) 



As usual, the experimental work of the year has largely been done 

 at the Alpine Laboratory from June 1 to September 15. Further 

 chemical determinations of the amount of rubber in native plants and 

 of the photosynthetic activity of various species have been made at 

 Tucson during the winter and spring. Studies of the regulatory 

 activity of stomata have been carried on at the Desert Laboratory and 

 at the laboratory of the American Smelting and Refining Company in 

 Salt Lake City for the purpose of checking the extensive results already 

 obtained. 



Vegetation studies have been made at Tucson during the winter and 

 upon four field expeditions from spring to autumn. The first of 

 these was through Arizona and California, and concerned itself chiefly 

 with the structure and extent of the bunch-grass and coastal sagebrush 

 associations, and with the charting and installing of permanent quad- 

 rats. The second traversed southern Arizona, New Mexico, Texas, 

 Oklahoma, Kansas, Nebraska, and eastern Colorado. It dealt chiefly 

 with the desert scrub and desert plains, and with the contact of the 

 latter and the short-grass plains. An exceptional opportunity was 

 afforded for studying the effect of grazing upon the subclimax, mixed 

 and true prairies, and their relation to the short-grass plains. The 

 third expedition was devoted primarily to the study of Bad Lands, and 

 such areas were visited in northeastern Colorado, western Nebraska, 

 western South Dakota, and Wyoming. In addition, the mixed- 

 prairie sagebrush community was examined over a wide area, and its 

 essential nature determined. Especial attention was given to the 

 fauna of the Bad Lands and the mixed-prairie climax. The fourth 

 expedition traversed southern Colorado, northern New Mexico, and 

 central Arizona, chiefly for Bad Lands, but partly also for the study 

 of variation in Artemisia, Chrysothamnus, and Atriplex. 



FACTOR STATIONS. 



The factor stations at Pike's Peak remain the same as for last year, 

 namely, the plains station in the mixed prairie at 6,000 feet, the base or 

 montane station in Douglas fir at 9,000 feet, and the subalpine station 

 n Engelmann spruce at 11,000 feet. Factor stations were also main- 

 aixied in the grassland formation at intervals of a difference of 5 inches 

 in the annual rainfall. These were located at Nebraska City and 

 Lincoln (Nebraska), Phillipsburg (Kansas), Burlington and Colorado 

 Springs (Colorado). At Lincoln, substations were also maintained in 

 high and low prairie. In the grassland series, the factors measured 

 were humidity, evaporation, water-content, air and soil temperatures. 



