462 
Journal of Agricultural Research 
Vol. XXXI, No. 5 
GROWTH UNDER ARTIFICIAL LIGHTING 
In order to test the converse side of this problem it was next pro¬ 
posed to learn whether active growth in the night could be checked by 
exposing the tree to artificial lighting. Electric wires from a lighting 
circuit of 110 volts were carried to the dark cell and two 200-watt in¬ 
candescent bulbs and two 60-watt bulbs installed, giving an illumi¬ 
nation of 520 watts. At 2.53 p. m. May 24, as shown by Graph III, 
in Figure 3, the dark cell was closed around the tree and active growth 
was recorded in about 25 minutes. After this growth in darkness had 
progressed till 9 p. m., the lights were switched on and kept burning 
till 3.40 a. m., though the dark cell was retained in position till 9 
a. m. The gain in growth was practically uniform through the entire 
period of nearly 18 hours. No checking of growth could be traced 
to the effect of this degree of illumination. A preliminary trial had, 
in fact, shown that the cell of 300 cubic feet of space was rather 
feebly lighted owing to the absorption of light by the black walls. 
Yet the same number of watts brilliantly illuminated the station 
office room, 22 by 16 by 10 feet high, or more than 10 times the cubical 
capacity of the dark cell. The dark cell was next lined with heavy 
white cotton sheeting and the lighting increased to six 200-watt 
bulbs, or 1,200 watts. The dark cell was closed at 5 p. m. May 27 
and active growth was registered at 6 (Graph III). At 9 p. m. the 
lights were switched on. This was followed by no growth for two 
hours or until 11 p. m. At this point the growth was resumed and, 
until the lights were switched off at 3.15 a. m. May 28, continued 
at practically the same rate of growth as in full darkness until the 
dark cell was removed at 3.15 p. m. May 28. 
This experiment was repeated in June under the supervision of 
Bruce Drummond. The lighting was increased to 1,800 watts and 
the dark cell was erected around the palm on June 15 and normal 
darkness growth began to be registered shortly after 7 p. m., as shown 
in Graph Y, a in Figure 3. At 9 p. m. (6) lamps to the volume of 
1,800 watts were switched on and continued until 5.30 a. m. of the 
16th (c). The gain made during these eight hours of illumination 
was only 3 mm., but from the time the lights were switched off till 
9 a. m. of the 16th (3.5 hours) a gain in the dark cell of 3 mm. was also 
made. In other words, the growth during the eight hours of intense 
illumination was at the rate of 0.375 mm. per hour, while that during 
the ensuing 3.5 hours of complete darkness was at the rate of 0.857 
per hour. The illumination reduced the growth rate to 43.7 per cent 
of the rate in darkness. Consequently even so vivid an illumination 
as that given by 1,800-watt incandescent lamps within this small 
space of 300 cubic feet, while slowing down the growth rate to less 
than half, fails to give the complete check which is observed in the 
ordinary intense sunlight of this station. Evidently a difference in 
the quality of the rays from the incandescent lamps and those from 
the sun must be more important than their difference in intensity. 
The facilities of the Indio field station could take the work no further. 
LABORATORY WORK AT WASHINGTON D. C. 
A laboratory opportunity for testing the action of date palms under 
light of a different quality was afforded by the presence in one of the 
department photographic rooms of two powerful “ Cooper-Hewitt” 
