DEPARTMENT OF BOTANICAL RESEARCH. 87 



ber of plants. This work clearly indicates that the index of foliar 

 transpiring power is a criterion by which the xerophytism or drought 

 resistance of plants (as far as their leaves are concerned) may be quan- 

 titatively approximated. The main results will appear in an article in 

 the Journal of Ecology. Mr. Bakke has carried this study still farther 

 during the summer of 1914, at the Desert Laboratory. 



Permanent Standardization of Cobalt-chloride Paper for use in measurhig 

 the Transpiring Power of Plant Surfaces, by B. E. Livingston and 

 Aleita Hopping. 



Further study of the conditions determining the time required for the 

 color change of hygrometric paper over the standard water-supplying 

 surface, carried out by Miss Aleita Hopping, at the Laboratory of 

 Plant Physiology of the Johns Hopkins University, has shown clearly 

 that this time-period is determined, for a given sample of cobalt-chloride 

 paper, by temperature alone, and that the length of this period is 

 inversely proportional to the maximum vapor pressure of water corre- 

 sponding to the given temperature. This point, which has long been 

 suspected, makes it possible to omit from the field observations all 

 reference to the standardizing water-test; simply the air temperature 

 (or preferably that of the leaves) is to be recorded instead. Each slip 

 of hygrometric paper is to be standardized in the laboratory, at a 

 known temperature, and from this observed time-period is to be calcu- 

 lated the time-period required for color change by the same slip at any 

 other temperature. A table of relations between temperature and 

 length of time-period is readily prepared, thus reducing the calculation 

 to a minimum for field-work. This advance removes the most trouble- 

 some features of the method and renders it much more readily adapt- 

 able to the needs of field ecology and agriculture than has been the case. 

 Other improvements in the technique of the method have been accom- 

 plished which will be set forth in a journal article. 



PHOTOLYSIS, RESPIRATION, HYDRATATION, AND GROWTH. 



Periodic Variations of Respiratory Activity, by H. A. Spoehr. 



The continuance of the study of the influence of light on living plants 

 is revealing more and more the extreme complexity of these reactions. 

 It is hoped, by means of a careful study of the chemical and physical 

 reactions induced by light in the organisms and in vitro, that the 

 explanation of physiological light reactions may be found, and that 

 ultimately certain climatological effects may be interpreted on this 

 basis. This analysis is revealing the fact that the quality of the light 

 (wave-length and intensity) is of great importance for a thorough 

 investigation of the subject, requiring a large amount of preliminary 

 work in other fields. 



