426 BOTANICAL GAZETTE [DECEMBER 
continued, the matters considered in the present paper forming 
a portion of our operations. Without the enthusiastic cooperation 
of Dr. Brown, the amount of experimentation and other work 
accomplished would have been much smaller, and the quality less 
satisfactory. 
In the three series of tests to be presented, the plants stood upon . 
a table in the open, the instruments being arranged in their imme- 
diate vicinity, so that the whole group of plants and instruments 
occupied a space perhaps 40 or so cm. square. Reduced light 
intensities were obtained by placing over the group, at a height of 
something less than a meter above the table, a cloth screen about a 
meter square, supported by a light wood frame and four light wood 
supports at the angles, The screen was always so placed that all 
the objects of the experiment were well within the shadow; they 
never received any direct sunshine while the shade was in position. 
The burettes of the atmometers and the tube of the radiometer 
projected below the table, so that the active portion of all instru- 
ments was always at approximately the same height from the table 
(and distance below the screen) as the plant foliage. The plants 
were 10-20 cm. in height; they had been lifted from the open soil 
several weeks previously and had been carefully accustomed to 
full sunlight. All had grown appreciably since potting, were 
leafy and apparently in good condition. They were in tinned sheet 
iron cylinders, some 8 or 10 cm. in diameter and about as high, 
- which, during the experiments, were sealed by the application of 
prepared modeling clay over the soil surface and over the drainage 
openings at the base. 
The plants were weighed and the instruments read at intervals 
of one-half hour, or as nearly so as possible. Where the time 
period was greater or less than 30 minutes, the data have been 
corrected to this time period. Weighings were made in the house, 
each plant remaining out of its proper position only long enough 
for this operation. In every test, after two half-hour periods of 
sunlight, there followed two similar periods under shade, these 
being in turn followed by two more periods of sunshine. The 
black bulb thermometer was covered most of the time by a loosely 
fitting cylinder or sheath of asbestos board, open at both ends to 
