22 WILTING COEFFICIENT FOR DIFFERENT PLANTS. 



Table VII. — Summary of wilting coefficient for seedlings and old plants. 





Crop. 



Seedlings, 



Old plants. 







Number of 

 observa- 

 tions. 



Mean 



wilting 



coefficient. 



Number of 

 observa- 

 tions. 



Mean 

 •wilting 



coefficient. 



Corn 





75 



06 



48 



626 



46 

 60 

 19 

 21 

 44 

 119 

 17 

 20 



1.03 

 .98 



.97 



.994 



.995 



.97 

 .94 

 .94 



.96 

 1.01 



.99 

 1.06 







Sorshum 







Millet 







Wheat 



Oats 



27 



0.98 



Barlev 







Rve 









Rice 









Grasses 



Legumes 



Cucurbits 



33 



19 





1.00 



1.02 



Tomato 









Colocasia 



19 

 8 





1.13 



Hydrophytes ! 







1.10 



Mesophytes . 

 Xerophytes . 



Weighted mean . 



1.00 . 



1.02 

 1.06 



EFFECT OF ENVIRONMENTAL CONDITIONS ON THE 



COEFFICIENT. 



WILTING 



A series of deterrninations has been made to ascertain the influence 

 of certain environmental conditions, particularly humidity, Light 

 intensity, and soil-moisture content upon the wilting coefficient. 

 These determinations are given in Tables VIII, IX, and X, and 

 indicate that the wilting coefficient is not materially influenced by 

 the dryness of the air, by moderate changes in the solar intensity, or 

 by differences in the amount of soil moisture available during the 

 period of growth. 



HUMIDITY. 



Table VIII gives a comparison of the wilting coefficient obtained 

 for Kubanka wheat grown from the outset in a dry greenhouse and in 

 a glass damp chamber. All determinations were made with the 

 same soil. Considerable variation is shown in the individual obser- 

 vations, which is apt to be the case where plants are subject to 

 extreme conditions. The high determinations are probably due to 

 imperfect root distribution. The mean value of the two series of 

 determinations is the same, indicating that the wilting coefficient is 

 not influenced to an appreciable extent by the saturation deficit. 



A plant wilts when transpiration exceeds absorption. Transpira- 

 tion may be decreased by reducing the transpiring area as well as by 

 increasing the humidity of the air. Absorption may likewise be 

 increased by increasing the root area. Bergen ' has shown that 

 when plants grown under humid conditions are transferred to a dry 

 atmosphere they transpire water much more rapidly per unit area 



1 Bergen, J. Y. The Modifiability of Transpiration in Young Seedlings. Botanical Gazette, vol. 48, 

 1909, p. 282. 

 230 



