ECOLOGY. 389 



ECOLOGY. 



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

 reports see Year Books Nos. 16-19.) 



The experimental work of the year has been centered at the Alpine 

 Laboratory from June 1 to September 15, and instrumental and aera- 

 tion studies have also been carried on there through the autumn and 

 winter. Determinations of rubber-content have been made at the 

 Desert Laboratory' during the winter and spring, and the histological 

 investigation of laticiferous tissue has been conducted at the University 

 of California. Statistical and garden studies in connection with ex- 

 perimental evolution have been made at the same institution, while the 

 researches in the absorption of water and nutrients by roots have been 

 carried on at the University of Nebraska. Stations for investigations 

 in experimental vegetation and in crop ecology have maintained as 

 heretofore at Peru, Nebraska City, and Lincoln (Nebraska), Philips- 

 burg (Kansas), and Burlington and Colorado Springs (Colorado). 



During the autumn and winter taxonomic studies in connection with 

 the monographs of Artemisia, Atriplex, and Chrysothamnus were 

 pursued at the Gray Herbarium, New York Botanical Garden, and 

 the National Herbarium. 



Vegetation studies were continued in the vicinity of Tucson during 

 the winter, and were also given major attention on three field expedi- 

 tions. The first of these was through Arizona and southern California, 

 and dealt chiefly with the contact between bunch-grass prairie and 

 coastal sagebrush, and between the latter and the desert scrub, with 

 dune communities, and with the distribution and amount of rubber 

 plants, especially Asclepias suhulata. The second traversed southern 

 Arizona, New Mexico, northern Texas, Oklahoma, Kansas, Nebraska, 

 and eastern Colorado. It concerned itself with the ecotone between 

 desert scrub and desert plains, and between the latter and the short- 

 grass plains, and gave special attention to the presence of mixed- 

 prairie relicts in the short-grass plains, to the movement of Poa and 

 Andropogon from the subclimax into the true prairies, and to the 

 problems of dune and playa deposition. The third expedition was 

 concerned primarily with succession and sedimentation in Bad Lands, 

 the relation of grassland to the sagebrush associations, and the chart- 

 ing and installing of permanent quadrats. It traversed northern 

 Colorado, southern Wyoming, Utah, Idaho, Oregon, California, and 

 Arizona. In addition, a journey was made through the northern 

 Rockies, the Cascades, and the Sierra Nevada for the purpose of 

 studying variation in Haplopappus. 



FACTOR STATIONS. 



The factor stations at Pike's Peak have been changed from the series 

 of zonal climaxes, and installed in two series, one climax, the other serai. 



