PERMANENT WILTING IN PLANTS 91 



wilted condition. If however, recovery did occur within twenty- 

 four hours, this was considered proof that permanent wilting had 

 not yet been attained. At the end of the test period the seals were 

 removed, the openings made in removing soil samples were re- 

 filled, the plants were revived by application of water to the soil, 

 and the cultures were returned to the general stock for further 

 recovery and use in subsequent experiments. 



EXPERIMENTATION 



Several preliminary experiments dealt with the question 

 whether the percentage of residual moisture left in a given soil 

 by maize plants at various stages of development was sensibly 

 constant when wilting occurred under similar atmospheric con- 

 ditions. Plants twenty days old left residues only slightly greater 

 than the residues remaining at permanent wilting of much older 

 individuals. With other plants twenty-eight days old, whose root 

 systems seemed to be well developed and equally distributed 

 in the soil masses of the cylinders, the soil moisture residues at 

 permanent wilting were not appreciably different from those 

 obtained with plants six or eight weeks of age. It thus appears 

 that, within these limits at least, the stage of development of 

 maize plants is not an important factor in determining the 

 moisture content in question. The other forms here employed 

 were not tested in this regard. The question here raised is, 

 however, not a vital one in the present study, for all the plants 

 used in any experiment were of the same age and had grown side 

 by side under the same environmental conditions. All were 

 apparently healthy. 



In the consideration of the experimental data it is to be borne 

 in mind that some error must result from the more or less pro- 

 nounced inability of the observer to fix upon the exact attain- 

 ment of the condition of permanent wilting. Error from this 

 source results, however, only when wilting is allowed to proceed 

 too far, since plants which have not attained the permanently 

 wilted condition revive without watering when placed in the moist 

 chamber for twenty-four hours. No such test can be applied 



