VOLUME LXVIII NUMBER 6 



THE 



Botanical Gazette 



DECEMBER igig 



RELATIVE TRANSPIRATION OF CONIFEROUS AND 

 BROAD-LEAVED TREES IN AUTUMN AND WINTERS 



J. E. Weaver and A. Mo gen sen 



(with eighteen figures) 



Introduction 



Transpiration has been of special interest to many investigators 

 for a long time. At first it was considered without reference to 

 environmental factors, but later, as more observations were made 

 and these factors were noted to have a marked effect upon the water 

 loss, they were taken into consideration. Many of the data 

 assembled have been Hmited to plants during the growing season, 

 so that it has seemed profitable to obtain not only quantitative 

 data on winter losses, but also a comparison of the relative transpira- 

 tion of conifers and broad-leaved trees in summer and winter. 



Various methods have been devised for determining transpira- 

 tion, from the cut shoot potometer, which usually gives losses quite 

 too low when compared with rooted plants (6, i6), to the cobalt 

 chloride method of Stahl (17), recently improved by Livingston 

 and Shreve (13). With few notable exceptions, such as the 

 method used by Iljin (ii), who worked on xerophytes and meso- 

 phytes in the field, the former method has been used largely for 

 laboratory measurements, while the latter, although especially 

 devised for field use, does not take into account the environmental 



' Contribution from the Department of Botany, University of Nebraska, new 

 series, no. 29. 



393 



