Bailey's experiments with other market-garden crops and flowers under glass gave varying results which, on the whole, were not encouraging, the light in some cases not producing much modifica tion, while in others modifying them in an unde sirable way. Some of the unfavorable results which he noticed were a spindling growth, a bleaching of some of the leaves, disintegration of the cells and a collapse of the chlorophyll bodies ; but these injuries are lessened or prevented by the inter position of clear glass, which cuts off the ultra violet rays.
W. W. Rawson, a Boston market-gardener, has employed electric light for some years in connec tion with his lettuce business, and has reported beneficial results from the use of an arc light sus pended over his houses.
Bonnier, of the University of Paris, has investi gated extensively the effects of electric light on plants and has arrived at many interesting con clusions which are not at variance with those of other experimenters. He found that electric light contains more of the ultra-violet rays, which can be screened out or weakened by the use of thick glass, and that plants illuminated by screened electric light differed widely from those cultivated normally, as well as from those cultivated under an intermittent light,—twelve hours of darkness and twelve of light. According to his observations, plants grown entirely under electric light possessed much greater quantities of chlorophyll, and even the deeper-lying tissues not normally possessing chlorophyll were green. The axes of plants were also shorter than those grown under normal con ditions, the leaves smaller and thicker and the flowers normally developed but more highly col ored. The internal structure of such plants strongly resembled etiolated plants ; that is, the me chanical tissues were not well differentiated. On the other hand, he found that plants exposed to discontinuous electric light showed some abnormal symptoms, but, in general, they possessed similar characteristics to plants grown in sunlight. It is thought that an uninterrupted duration of illumi nation is responsible for the deviation from the normal structure.
Bonnier made comparisons with plants grown in northern latitudes and those grown on the moun tains of central Europe, and he maintains that the plants of northern latitudes possess less differen tiation of structure than those in the mountains of central Europe. and that the same species of plants grown in continuous light resemble those which are found in the polar regions.
Electric incandescent light.
Bane experimented with incandescent light, the results of his work appearing in Bulletin No. 37 of
the West Virginia Experiment Station. His results appear to be very similar to those secured by Bailey and others with the arc light.
The essential difference between the arc light and the incandescent light in this connection is that in the arc light the chemical or actinic rays are prominent, while in the incandescent light these are only slightly present. The spectrum of the in candescent light is that of carbon at low intensity, the luminous part of the lamp being cellulose ; it is modified somewhat by the glass of the bulb. The incandescent light is much steadier than the arc, and it casts no sharp shadows ; it is less expensive and requires almost no care. Rene found (1) That the incandescent electric light has a marked effect on greenhouse plants.
(2) That the light appears to be beneficial for some plants grown for foliage, such as lettuce. The lettuce was earlier, weighed more and stood more erect.
(3) That flowering plants blossomed earlier and continued in bloom longer under the light.
(4) That the light influences some plants, such as spinach and endive, to run quickly to seed.
(5) That proper watering appears to be more important with radishes, beans and cuttings than improper watering plus the electric light.
(6) That the stronger the candle-power the more marked the results, other things being equal.
(7) That most plants tended toward a taller growth under the light.
Acetylene light.
The use of acetylene light for forcing plants has not yet had sufficient study to justify positive assertions regarding its value. Perhaps the mo=t important investigations were those made at the Cornell Experiment Station in 1905 and 1906, and reported by John Craig, in the "Acetylene Journal" for September, 1906. The following discussion is an abstract from this report. (The full report, in bulletin form, to be made by the Cornell Station, is pot published as this article is written) : The chief interest in the use of acetylene light for forcing plants, centers about the fact that in its composition it more nearly resembles sunlight than any other artificial illuminant in use. It is composed of the same colors and in very similar degrees of intensity. Miinsterberg makes the fol lowing comparison of color values of acetylene and sun rays, allowing 1 to equal the value of each color of sunlight : Indigo and orange are not given. The ultra-vio let rays, the injurious factors in the case of electric light, are practically absent in acetylene, although blue and violet are equally strong.