342 CARNEGIE INSTITUTION OF WASHINGTON. 



while wind and light intensity were also measured in the mountain 

 series, together with rainfall. For determining the variations in light 

 intensity with the altitude, as well as with the season and time of day, 

 a full battery of recording photometers was installed at the three sta- 

 tions for the first time. These employed Azo paper for a record and 

 consequently were checked by hourly readings made by means of the 

 stop-watch photometer on Solio paper, which has now been in use for 

 this purpose for more than twenty years. 



The Phytometer Method, by F. E. Clements, J. E. Weaver, and G. W. Goldsmith. 



The use of phytometers, or standard plants, to measure habitats in 

 terms of plant response and growth, has now been carried through 

 three summers. The stations, equipment, and species are the same 

 as those employed in 1919, except that photometers have been used to 

 evaluate the light differences. The method of sealing the phytometer 

 cans by means of hard wax melted onto cloth covers was used again 

 with satisfactory results, although the season proved extreme in many 

 ways. An endeavor was made to have the soil and seed as nearly 

 identical as possible with that employed in 1918 and 1919. 



The instruments were read each week, soil temperature and water- 

 content determined, and each plant weighed and its water-loss com- 

 puted. For the sunflowers an empirical formula for obtaining the leaf 

 area from the product of the maximum width and length was worked 

 out, and by its use the leaf area of each plant was computed weeklj^ 

 The monocotyl leaves were considered as triangles and their weekly 

 area computed on that basis. In addition to leaf area and water-loss, 

 the stem height and diameter were obtained weekly for the sunflowers. 

 For each sealed phytometer a check was grown under identical condi- 

 tions, except that it lacked the seal. In addition, garbage cans holding 

 about 75 pounds of soil were used both as phytometers and checks. 

 The plants in them were grown through the season to the period of 

 fruiting. These were used partly to determine the time during which 

 normal behavior could be expected from the plants grown in the one- 

 gallon containers. 



The first series of phytometers was run from June 9 to July 19. 

 During this time the plains station showed higher average temperature, 

 greater fluctuation between average day and night temperature, less 

 average rainfall, greater average evaporation from atmometers, greater 

 average night but less average day humidity, and greater average wind 

 movement than the other two stations. The subalpine station in 

 general showed conditions opposite to those at the plains station, while 

 the montane base station was usually intermediate. 



The sunflowers show a relative increase in height roughly pro- 

 portional to the elevation, but the stem diameter increases most 

 rapidly at the base station. The leaf area, though slightly greater at 



