630 BOWMAN— ECOLOGY AND 



desiccator, which was cooled artificially by an ice chamber about it. 

 This was found necessary to expedite the taking of tests, as the heat 

 absorbed by the apparatus during the drying had a vitiating effect 

 on the transpiration experiment unless cooled, and if allowed to cool 

 to the room temperature slowly, too much time was lost between 

 tests. After a minute or two, the apparatus, sufficiently cooled and 

 dry, was quickly removed from the desiccator and clamped on the 

 upright rod support beside the culture jar, the selected leaf placed 

 in the clasp and the screws slightly adjusted to press the sides of 

 the clasp on the surfaces. By a stop watch the time was then 

 noted that was required to change the color of the indicator disc to 

 a uniform pink, due to the effect of the moisture transpired through 

 the stomata and epidermis of the leaf. As there are no stomata on 

 the upper surface the change in color for the disc on the upper 

 side of the leaf always lagged in the time interval from 65 to 80 

 seconds behind the lower or stomatal side. This interval was con- 

 stant for nearly all tests and for this reason only the lower-side 

 indicator was used for the records. An error in calculating the 

 time interval required to effect the change in the indicator occurs 

 in the loss of time required to adjust the instrument on the plant, 

 during which the atmosphere has an opportunity, for a few seconds, 

 to get in its influence on the instrument, but the transfer from the 

 desiccator to the plant becomes routine after a few hundred tests 

 and this time error of a few seconds may be disregarded, as it is 

 constant for all the tests. 



The successive tests were made at one time on each culture jar, 

 separate leaves, one each, of the three plants in the jar being used. 

 The time of taking the tests was as far as possible made in the mid- 

 dle portion of the day and every effort was made to avoid jarring 

 or shocking the plants just before or during a test, on account of 

 the accelerating effect of shock on the transpiration rate. The 

 records were all marked in notebooks and the average taken for 

 the three tests on one culture jar. 



The cultures were kept on large tables holding about thirty jars 

 in the laboratory, which was open on all sides and contained venti- 

 lator trap doors in the roof which were propped open during the 

 day. The plants were thus sheltered from the direct rays of the 



