A QUANTITATIVE STUDY OF TRANSPIRATION 



Grace Lucretia Clapp 



GRAPHS 



In the Laboratory of Plant Physiology of Smith College a system- 

 atic series of studies is being made to determine which of the plants 

 available to American teachers are best for the demonstration^ or 

 investigation, of each of the principal physiological processes, and how 

 much may be expected of them. Some of theec studies in physiologi- 

 cal constants have already been completed and others are well under 

 way, I have undertaken to determine these facts for the process of 

 transpiration. This work has been done under the direction of Pro- 

 fessor W. F. Gaxoxg, whose advice and supervision I gratefully 

 acknowledge* 



Transpiration has been extensively investigated from several points 

 of view, and the results up to 1904 are all summarized in Burger- 

 stein's admirable monograph.' It shows that investigations have 

 been directed mainly to explain the amounts of transpiration as depend- 

 ing either upon structural features or upon physiological processes, 

 or as controlled by physical changes. Special work now being done 

 by Livingston, Lloyd, and others at the Carnegie Desert Labora- 

 tory in Arizona is hkely greatly to extend our knowledge of transpira- 

 tion as an ecological factor in the plant hfe of the desert. But nothing 

 has as yet been done in the direction of the present study. I have 

 not been concerned with the explanation of transpiration upon either 

 a physical or a physiological basis, nor yet with the relations between 

 absolute and relative transpiration, but simply with the fact that 

 plants lose appreciable amounts of water. I have sought to deter- 

 mine with precision the actual amounts of water lost by plants, grow- 

 ing under the ordinary conditions arising in any greenhouse, and 

 simultaneously have determined the transpiration under conditions 

 which admit of control and repetition. 



, My procedure was as follows. In each species studied, two well- 

 grown plants, of as nearly the same size as could be found, were 

 chosen at maturity, when increase of leaf surface is at a minimum. 



' EURGERSTELV, ALFRED, Die Transpiration der Pflanzen. Jena. 1904- 



Botanical Gazette, vol. 45] [25-t 



«^ 



