318 



AMERICAN JOURNAL OF BOTANY 



[Vol. 9, 



total dry weight was slightly greater in the plants grown in the dry atmos- 

 phere. The total ash content was only slightly greater, 147 milligrams 

 per culture in the plants grown in the dry atmosphere as compared with 

 135 milligrams per culture in the plants grown in the humid atmosphere. 

 The total ash expressed as percentage of dry weight was only about five 

 percent less (ratio of dry to humid = 100 : 94.7) in the plants grown in the 

 humid chamber than in those grown in the dry chamber. The ash, ex- 

 pressed as percentage of green weight, was about fourteen percent less 

 (ratio of dry to humid = 100 : 86.4) in the plants grown in the humid 

 chamber. 



Table i. Relation of Ash Content in Barley Plants to the Amount of Transpiration as 



Affected by a Difference in Atmospheric Humidity. Summer Series. 



Plants Grown 5 Weeks {August 4 to September 8, 1Q20) 



Dry Chamber 



Tops 



Roots 



Plants 



Humid Chamber 



Tops 



Roots 



Plants 



No. of cultures averaged 



Green weight per culture (grams) 



Dry weight per culture (grams) . 



Total ash content per culture 

 (grams) 



Ash content (percentage of green 

 weight) 



Ash content (percentage of dry 

 weight) 



Total water transpired (cc.) . . . . 



Water used per gram dry matter 

 (cc.) 



Water used per gram ash con- 

 tent (cc.) 



6.5 

 .60 



•125 

 1.92 

 20.7 



2.2 

 .11 



.022 



1. 00 



20.02 



25 



8.7 

 •71 



.147 



1.69 



20.63 

 350 



492.96 

 2,380.95 



7.206 



•5854 

 .116 



I.6I 



19-63 



2.067 

 .1068 



.019 



.90 



18.07 



25 



9.270 

 .6922 



■135 



1.46 



19-54 

 170 



245-59 

 1,259-25 



The data show that by increasing the atmospheric humidity the quan- 

 tity of water transpired was reduced from 350 cubic centimeters to 170 

 cubic centimeters per culture for the period of five weeks. This reduction 

 in transpiration also correspondingly reduced the water requirement from 

 492 to 245. The quantity of water transpired per gram of ash content 

 found in the plants was also reduced to approximately one half when trans- 

 piration was reduced. These data seem to check with those reported by 

 Hasselbring (1914 a), Kiesselbach (1916), McLean (1919), and Curtis 

 (1920), indicating that there is no direct relation between transpira- 

 tion and the ash content in plants. 



The fact that the absolute quantity or percentage of ash is reduced but 

 slightly when transpiration is reduced to less than one half seems significant 

 evidence against the theory that there is a direct relation between trans- 

 piration and the absorption of salts. Even the slightly greater ash content 

 of the plants in the dry chamber seems to be determined by some factor 

 other than the amount of water absorbed, namely food supply, which will 



