(6) The range of the light was somewhat vari able for the different crops. In general, the maxi mum growth was attained at twelve to sixteen feet from the light, while a perceptible increase was noted at twenty-four feet.
17) Bloom record of tomatoes showed markedly earlier bloom in the light house,— eight days the least and eighteen days the greatest difference.
(8) In the case of radishes, top growth was stim ulated, hut evidently not markedly, at the expense of root. With sugar-beets, top growth was greatly stimulated, evidently at the expense of root growth.
(9) While the roots of beets grown in the nor mal house were larger than those in the light house, the sugar contents and the percentage of purity were markedly higher in the light-house grown plants.
(10) Spinach, lettuce and radishes all tended to make seed-stalks earlier under the light.
(11) Lettuce and spinach under the influence of the incandescent gaslight not only grew faster during the growing period, but the period was actually longer than for plants in the normal house.
The Cooper-Hewitt mercury vapor electric light.
C. P. Close, of the Delaware Experiment Station, endeavored to determine the effect of the Cooper-Hewitt mercury vapor electric light on plants. The re sults of his work were presented before the Society for Horticul tural Science, at its second annual meeting, and are recorded in the proceedings of the society.
In conducting this test it was necessary to have an enclosed place practically light-tight, so as to ex clude the daylight and allow the plants to have the artificial light only. This was provided by build ing in the greenhouse a " double deck " bed, using the upper bed for plants in sunlight and the lower bed for those in artificial light. The lamps used were the Cooper-Hewitt 4-H pattern. These were suspended as nearly over the center of the bed as possible. Owing to variation in the electri cal potential — from 100 to 125 volts —a constant intensity oflight could not be maintained.
The light from these lamps is perfectly white, devoid of red rays. The candlepower of a 4-H lamp, or tube, is about 650, and the expense per candle-power is about one-eighth that of the candle power of the incandescent electric light, and about three-fourths that of the arc light. The light is
caused by the vapor of mercury in the tube becom ing heated white hot as the electric current is passed through it. One end of the lamp-tube is positive, the other negative, and the vapor of mer cury completes the circuit by connecting the two.
Tests were made with lettuce and radishes. Over the lettuce at first only one lamp was used, placed about sixteen inches from the soil. The growth was unsatisfactory because of the unfavorable tem perature and atmospheric conditions of the bed, due to the tight enclosure, allowing no ventilation. The excess of moisture that accumulated in the atmosphere was a great hindrance. The plants received light only during the night. They partook of the nature of twining plants. The stems were long and produced leaves at intervals of two or three inches ; and not being strong enough to sup port their weight, assumed a recumbent position. It was impossible to keep plants alive for any length of time when they were more than two or three feet beyond the end of the lamp-tube. The time germination was the same as for seed sown in daylight. The formation of chlorophyll seemed to be perfectly normal. After a few weeks the plants came practically to a standstill. With two lamps, the results were but little more en couraging.
The results with radishes were practically the same. There was no fleshy root development, and the plants were long and weak. There was very little leaf-growth, although there was production of chlorophyll.
These experiments must be considered prelimi nary. They demonstrated that chlorophyll could be formed by this light, devoid of red rays. With im provement in the electrical apparatus better results are to be expected.
Influence of colored light on plants.
Investigations pertaining to the effects of the dif ferent rays of light on plants have been conducted for many years, although many of the earlier ex periments are more or less faulty, since pure spec trum colors were not always employed, nor were the plants always subjected to the same degree or intensity of light.