THE ROLE OF TEMPERATURE IN THE DETERMINA- 

 TION OF THE TRANSPIRING POWER OF LEAVES 

 BY HYGROMETRIC PAPER 



EDITH BELLAMY SHREVE 



Desert Laboratory, Tucson, Arizona 



In the investigation of the transpiration of plants there are 

 obvious advantages in being able to determine the rates of water 

 loss from the leaves of entire plants growing in the soil or in their 

 natural habitats, as contrasted with the use of severed shoots or 

 potted plants. This advantage has led Livingston to revive the 

 cobalt chloride method of Stahl, in which dried slips of paper 

 impregnated with this salt are placed next to the leaf and the 

 time is observed which is required for the change from blue to 

 pink. Livingston 1 has improved the technique of Stahl' s method 

 and has provided for the standardization of the readings secured 

 by ascertaining the time required for the color change over a free 

 water surface. A further improvement in the method has been 

 made by Livingston and Shreve 2 in the devising of a tripartite 

 slip, in which pieces of paper of two shades of fixed blue are 

 placed alongside the piece which is subject to color change. The 

 attainment of a uniform color change in all tests is thereby 

 ensured. 



One of the greatest problems in employing this useful method 

 has arisen from the important influence that temperature has 

 upon the rate of absorption of moisture by cobalt chloride. 

 The solution of this problem, with the exception of one difficulty, 

 has been given by Livingston and Shreve. 3 This difficulty is 

 described by them as follows: 



1 Livingston, B. E., The resistance offered by leaves to transpirational water 

 loss. Plant World, 16: 1-35. 1913. 



2 Livingston, B. E. and Shreve, E. B., Improvements in the method for de- 

 termining the transpiring power of plant surfaces by hydrometric paper. Plant 

 World 19: 287-309. 1916. 



3 Livingston, B. E. and Shreve, E. B., Idem. 



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