1908] 



CLAPP— STUDY OF TRANSPIRATION 



255 



Two or three clays before use^ these were brought into the experi- 

 mental greenhouse, where conditions of heat, moisture, and light 

 Were practically the same as in the greenhouse proper. Any plant 

 likely to be pot-bound was repotted in the soil mixture for common 

 plants two or three weeks before the test, in order that 

 become properly adjusted. 



The actual transpiration w^as determined throughout by the most 

 accurate known method, that of weighing. To prevent evaporation 



it might 



p^ 



V u 



■J V ' '^ 



'J^JtLr 



1 V iz^jj *-•- 



Fig. I 



from the pot and soil, each pot was- covered by an aluminum or zinc 

 shell of proper size, roofed over by rubber sheeting. This was tightly 

 clasped to the plant, cemented along the seam, and fastened to the 

 shell by a metal band, removable to permit the plant to be watered. 

 The plant to be kept under greenhouse conditions was then placed 

 on a specially constructed balance which was brought into electncal 

 connection with the autographic transpirometer invented by Pro- 

 fessor Gaxoxg and described by him in this journal." The entire 

 arrangement, slightly modified from the original form, is well shown 



» G.\xoxG, W. F., New precision appliances for use in plant physiology. Box. 



G.\ZETTE 39:145. 1905. 



