322 



AMERICAN JOURNAL OF BOTANY 



[Vol. 9.. 



Table 4. Comparison of the Average Percentage of Ash Based upon the Green Weight of 

 Tops, Roots, and Total Plants {Averages of cultures in tables i and 2) 



Set of Cultures 



Dry. chamber 



Humid chamber 



Light 



Shade 



Percentage of 

 Ash in Tops 



1.92 ± .030 

 I.6I ± .022 



1.88 ± .028 



1.93 ± .031 



Percentage of 

 Ash in Roots 



1. 00 ± .024 

 .93 zfc .024 



2.01 zfc .046 



.9S ± .036 



Percentage of 

 Ash in Plants 



1.69 ± .026 

 1.46 ± .016 

 I.9I ± .019 

 1.68 ± .026 



Winter Series 



Light-Shade Cultures 



A series of cultures was set up during the winter in order to check the 

 results obtained by shading plants in the summer experiment. Table 5 

 presents a summary of the data obtained. The data are self-explanatory 

 and check very closely with the light-shade cultures of the summer series. 

 The absolute values for green weight, dry weight, and ash weight are slightly 

 lower throughout, but relatively the results duplicate those of the summer 

 series. The water requirement and the quantity of water used per gram 

 of ash content were increased considerably in the plants growing in the shade 

 under conditions of low transpiration. This relation holds not only between 

 the shaded and unshaded plants within the summer and winter series, but 

 also between the summer and winter series. The plants growing on an, 

 exposed greenhouse bench and in a shade tent in winter receive much less 

 sunlight than plants growing under similar conditions in the summer. 



Table 5. Relation of Ash Content in Barley Plants to the Amount of Transpiration as 



Affected by a Difference in Light Intensity. Winter Series. Plants 



Grown 5 Weeks {January ig to February 24., iQZi) 



Light 



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.) 



Shade 



This probably explains the increase in water requirement and in quan- 

 tity of water used per gram of ash content in the plants of the winter series. 



