88 J. W. SHIVE AND B. E. LIVINGSTON 



and had the advantage of only slightly injuring the root system; 

 thus it was possible to use the same plants again, for later exper- 

 iments, after the lapse of from ten days to two weeks, the opening 

 left in the soil mass by the removal of the sample being of course 

 refilled. The soil samples were collected directly into weighed 

 screw-cap bottles, and their moisture contents were determined 

 in the usual way, by drying to constant weight at a temperature 

 of from 102° to 104°C. 



As in the experiments of the earlier workers upon this subject, 

 it was necessary in these studies to provide a series of exposures 

 for the wilting plants, characterized by markedly different evap- 

 orating powers of the air. Since facilities for the adequate con- 

 trol of these environmental conditions, in the presence of day- 

 light, have still to be devised, the methods here employed were 

 very crude. These methods consisted merely in arrangements 

 by which the evaporating power of the air in inclosed chambers 

 was reduced to a greater or less degree below that prevailing in 

 the open. Of course this condition in the open was subject to fluc- 

 tuations, from day to day as well as from hour to hour of the same 

 day, and this consideration entails corresponding but less marked 

 fluctuations within the enclosures. The highest evaporating 

 powers of the air were naturally obtained in the open, where 

 the plants and instruments were exposed on a table constructed 

 of parallel-placed slats 8 cm. wide, with intervening openings of 

 the same width, thus allowing considerable opportunity for ver- 

 tical air movement. This table was 1 meter high and stood in a 

 freely exposed position, at least 15 meters from the nearest 

 building. Another exposure, partly shaded and partly shielded 

 from wind movement, was obtained upon a table in the lath 

 shelter previously mentioned. This is the lath shelter employed 

 by Brown and by Caldwell, it is about 5 meters square and 3 meters 

 high, the walls and top being mainly composed of parallel-placed 

 laths (about 3 cm. wide), with openings equal to the width of 

 a lath. For still lower evaporating powers two cheesecloth 

 chambers were constructed, by stretching the cloth over wooden 

 frames to make cubical enclosures a meter in diameter. The 

 walls and top were of cloth and the bottom of thin sheet iron. 

 The bottom was 75 cm. above the ground. In these cloth cham- 



