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



The data characterizing the atmospheric conditions for each 

 of the different exposures employed were recorded at intervals 

 of two hours. .Temperatures were obtained from shaded ther- 

 mometers. The evaporating power of the air was automatically 

 summed for each two-hour period by means of the porous cup 

 atmometer, operating from a burette as reservoir; for convenient 

 reading the burettes were placed outside the various chambers. 

 The readings were corrected in the usual way, to give aver- 

 age rates for the periods in question, in cubic centimeters per 

 hour. Eelative humidity readings were obtained from hair 

 hygrographs, though these were omitted in a number of cases 

 where but one or two plants became permanently wilted during 

 a period. The readings of these instruments showed that there 

 were, for any given period of a few hours, but small differences 

 in temperature between the several exposures described above. 

 They also showed, on the other hand, that the two cloth chambers 

 and the lath shelters offered three different evaporating powers 

 of the air intermediate in magnitude between the extremes offered 

 by the open and by the glass box. Data to be given in the next 

 section will present the quantitative aspect of this serial arrange- 

 ment. 



Each experimental series involved sixty cultures, in five groups 

 of twelve cultures each, one of these groups being subjected to 

 the conditions of each of the five different exposures. By the 

 exercise of care in selecting the cultures for each group, bringing 

 together only plants which had attained approximately the same 

 degree of development, it was possible to secure groups in which 

 wilting occurred in the majority of the plants during the same 

 hour of the same day. When several plants were included in 

 the same culture they all attained the permanently wilted con- 

 dition at about the same time, at least within the same two- 

 hour period. 



As soon as a culture appeared to be permanently wilted its soil 

 sample was taken, and the culture was then placed in the moist 

 chamber, to test the possibihty of recovery without watering. If 

 recovery did not then occur within a period of twenty-four hours, 

 the culture was considered to have been truly in the permanently 



