390 CARNEGIE INSTITUTION OF WASHINGTON. 



The former comprises the yellow pine, chaparral, and mixed-prairie 

 communities, and the latter the successional stages on the north and 

 south exposures of Engelmann Canyon. In these the factors measured 

 were humidity, air and soil temperatures, water-content, light, wind, 

 and evaporation, and the instrumental readings were supplemented by 

 batteries of phytometers. In addition, factor stations were maintained 

 at Peru and Lincoln (Nebraska), Phillipsburg (Kansas), and Burling- 

 ton (Colorado), as well as in several communities at Lincoln. Factor 

 instruments were also installed in the desert plain and foothill com- 

 munities of the Santa Rita Range Reserve south of Tucson during the 

 winter and spring for the purpose of studying the development of the 

 winter annuals and grasses. 



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



Phytometers, or standard plants, have again been employed in 

 connection with instrumental batteries to permit a closer analysis of 

 the efficient factors, and to furnish an integration of the habitat factors 

 as a complex. They have been used in the yellow pine, chaparral, 

 and plains climaxes, and in the various communities of the slope- 

 exposure investigation in Engelmann Canyon. In concluding the 

 preliminary study of the phytometer method, special attention has 

 been paid to checking the methods employed, kinds of plants used, 

 and their variability. Comparisons have been made of the effective- 

 ness of the various methods of sealing, not only for the purpose of 

 checking the results previouslj^ obtained, but also to improve the 

 methods for future use. The seals employed include the ordinary wax, 

 sheet-rubber, rubber-cement cloth, paraffin-cloth, casein-cloth, marine- 

 glue cloth, and modeling clay. Paraffin-cloth has been found to be best 

 adapted to field use under the conditions encountered at Pike's Peak. 

 Sheet-rubber is excellent for short periods, but all other seals permit 

 the entrance of water, with the exception of modeling clay. 



The accurate weighing of heavy containers in the field ordinarily 

 requires expensive apparatus that can be transported with difficulty 

 if at all. For this reason a balance has been devised that is simple in 

 construction and inexpensive, and that combines portability with 

 capacity and comparatively high sensibility. 



The variability in growth and transpiration per unit area has been 

 computed for the sunflower, bean, and a representative monocotyl 

 used as phytometers, in order to determine that the previous results 

 are not based upon mere variations in the behavior of individual plants. 

 With the present season the four-years development of the phytometer 

 method is completed, and the results are now being brought together 

 for publication. 



