16 



WILTING COEFFICIENT FOE DIFFERENT PLANTS. 





considerable variation in individual pots, the mean of a suitable 

 series represents the wilting coefficient of a given soil with an 

 accuracy equal to the accuracy with which the moisture retentivity 

 of the soil can be measured by purely physical methods. 



COMPARISON OF THE SOIL-MOISTURE CONTENT AT THE WILTING POINT 

 AND THE DEATH POINT. 



Emphasis has already been placed upon the fact that the wilting 

 point does not mark the minimum limit of moisture that is available 

 to the plant. The experimental data upon which this conclusion 

 was based are given in Tables II and III. Determ in ations were 

 made of the soil-moisture content at the wilting point and at the 

 death point for each individual culture. In every instance a marked 

 reduction of the water content was noted after the plants wilted. 



The data given in Table II were obtained with Kubanka wheat 

 seedlings grown in sealed pots. The pots were kept in a temperature- 

 control tank until the plants wilted. The weight of each pot was 

 then taken. Some of the pots were then transferred to a dark 

 constant-temperature room, while the remainder were left in the 

 control tank. After the plants had died, the pots were again 

 weighed and moisture determinations made upon the whole sample. 

 The difference in weight corrected for the loss in weight of the plants 

 gave the necessary data for calculating the wilting coefficient. 



Table 'II. — Comparison of the wilting coefficient and the water content at death -point 

 for Kubanka wheat seedlings in soil Xo. 26. 





Observation. 



Plants allowed to die 

 in temperature-con- 

 trol tank in green- 

 house. 





Observation. 



Plants allowed to die 

 in dark room at con- 

 stant temperature. 



















Wilting 



coefficient. 



Moisture 



content at 



death 



point. 







Wilting 



coefficient. 



Moisture 



content at 



death 



point. 



1 





M 



8.3 

 8,0 



8.3 

 8.1 

 8.3 

 8.3 



7. S 

 8.3 

 8.0 

 8.5 

 8.7 

 8.6 

 8.6 

 8.2 

 8.5 

 7.8 

 8.0 

 7.5 



7.3 

 7.4 

 7.4 

 7.1 

 7.4 

 7.5 

 7.9 

 7.5 

 7.5 



?:? 

 \\ 



b. i 

 7.5 

 7.8 

 7.5 

 7.3 

 7.3 



1 



8.5 

 8.1 

 8.4 

 S.l 

 7.9 

 S.O 

 8.2 



S.3 



9 



9 





3 





3 



8.0 



4 



4 



6.9 







7.3 



6 





6 







1 7 . 





R 





8.. 





8.5 

 7.9 



8.2 



q 



q 







10.. 



li.. 



12.. 

 13.. 

 14.. 

 15.. 

 16.. 

 17.. 

 18.. 

 19.. 















8.2 

 ± .05 

 ± .21 



7.5 



± .04 

 ± .18 



Mean 



Probable error of 



S.2 | 7.7 

 ± .05 + .10 





Probable error of 

 mean 



Probable error of 

 single observation. 





Probable error of 

 single observation. 



± .16 



± .30 



230 



