ECOLOGY. 303 



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



Sunflower phytometers have been carried through the season in three 

 habitats at the Alpine Laboratory, viz, full sunlight, partial shade, and full 

 shade. The initial rates of transpiration per leaf area were determined for a 

 large number of plants under identical conditions and the batteries for 

 the stations selected so as to have similar transpiration rates. Special con- 

 tainers were devised, shaped as two truncated cones base to base and equipped 

 with two half-inch tubes, one reaching nearly to the bottom, the other just 

 penetrating the metal of the top, in order to allow both top and bottom 

 watering and also to permit the soil atmosphere to be replaced by atmos- 

 pheric air. The conical form was chosen because of the reduced area left 

 for sealing and also because this form permits firming the soil with the least 

 possible interference. The wax-cloth seal was employed, with the addition of 

 a plastocene collar around the plant-stems to prevent injury from hot wax of 

 high melting-point. Each battery consisted of 10 plants, 2 blanks to check the 

 efficiency of the seal, and 2 free check plants. The physical instruments in- 

 stalled in each station showed the shade station to have greatly reduced light, 

 temperature, wind, and evaporation values and a very constant soil tempera- 

 ture, in comparison with those obtained at the sun station. The partial shade 

 gave values somewhat nearer those of the shade than of the sun station. 



The transpiration results from the phytometers yielded values for these 

 habitats which represented the summation of the factors measured partially 

 by the instruments. As to growth, the plants in partial shade exhibited greater 

 height, smaller stem diameter, and thinner leaves than those of the sun station ; 

 plants grown at the shade station were much smaller, both in stem diameter 

 and leaf area, than those at either of the other stations and also differed con- 

 spicuously in the succulence of the stems and leaves. Microscopic examination 

 of the leaves showed a very slight palisade development, the mesophyll being 

 chiefly sponge-tissue and wider than that of the leaves developed in partial 

 shade. Stomatal movement, pigment content, water conduction, and gas 

 exchange in the stems were also determined at each station. 



Short-period phytometers were also employed to measure the differences 

 between habitats in terms of single functions, such as transpiration. These 

 have the advantage of being much simpler to install and attend and of giving 

 much more accurate results, as smaller containers can be used and more 

 uniform conditions selected, as to time especially. Moreover, they are much 

 less subject to a wide variety of accidents, and the sealed plants can be main- 

 tained for periods of a few hours to several days in practically normal root 

 condition. Such batteries have been used with marked success for several 

 days in readings varying from 1 to 4 hours, for day and night, and for 24 

 hours, the conditions measured being light, slope-exposure, angle of slope, 

 radiation and reflection from different soils, and the altitude complex. The 

 results of the work of the four summers are now being prepared for publication. 



The final results obtained by the use of phytometers in the analysis of 

 marked differences in the physical factors and vegetation of north and south 

 slopes are indicated in the following section. The methods and results per- 

 taining to other forms of phytometers, namely, the sod core used for trans- 

 piration in natural grassland and the cut quadrat employed for the measure- 

 ment of seasonal growth, are discussed briefly in later sections. 



