GROWTH IN CONTINUOUS ILLUMINATION 719 



intensity. He described the effect of continuous illumination on plants 

 as a "green etiolation" (^tiolement vert) and stated that this compared 

 favorably with the structure and appearance of Arctic plants harvested at 

 Spitzbcrgen. 



Unfortunately Bonnier used only two light sources in his studies, 

 sunlight and the arc lamp. The arc lamp approaches sunlight very 

 closely in quality. The conclusion, therefore, that the structural 

 changes produced are independent of the nature of the light, in the sense 

 of quality or wave-length distribution, is not justified. Popp (20) showed 

 that removing the blue and all wave-lengths shorter than 5290 A from 

 sunlight produced a type of etiolation characterized by thin stems and 

 thin leaves, both poorly differentiated, structurally. Smith (27), using 

 both incandescent filament lamps and Arctic sunlight, compared barley 

 plants exposed continuously with those grown on shorter day lengths and 

 found no indication of "green etiolation." On the contrary, the green 

 tissue produced is described as "nicely green, but a little light" on the 

 6-hr. day plants and "deep and glossy green without any visible differ- 

 ence" in the 12-, 18-, and 24-hr.-day groups. The incandescent filament 

 lamp has much more red and infra-red and much less blue than either the 

 carbon-arc lamp or sunlight. Harvey (13) grew a number of varieties of 

 plants exposed continuously to filament lamps. Potato, tomato, and 

 other plants grown at an intensity of 380 lumens per square foot (380 

 foot-candles) grew well but were somewhat taller than normal, while 

 plants grown at an intensity of 680 lumens per square foot appeared 

 much more normal. Guthrie (12), using filament lamps, found that 

 either increasing the day length toward continuous illumination or 

 removing the blue region from the solar spectrum resulted in a decrease 

 in chlorophyll. Johnston (15) observed that plants grown under an 

 energy distribution including the visible and infra-red were not so green 

 as those receiving only visible light with the red region further decreased 

 by a red infra-red absorbing filter. Arthur recently grew buckwheat 

 plants for two weeks under continuous illumination, using in one case a 

 1000-watt incandescent filament lamp. Adjoining this, with only a sheet- 

 metal baffle between, a similar set of plants was grown under a 25-amp. 

 carbon-arc lamp. The tests were made in the constant condition room 

 at the Boyce Thompson Institute for Plant Research. An attempt 

 was made to adjust the distance of the two lamps so that the total 

 energy at the soil level was the same. On account of the inconstancy of 

 the flaming arc and the deposit of inorganic material from the carbons on 

 the glass globe enclosing the arc, it was found impossible to maintain the 

 same total energy relations. The intensities, how^ever, were comparable. 

 The leaves of the plants grown under the filament lamp were light 

 green in color in contrast with those grown under the arc lamp which were 

 very dark green in color. It is certain, therefore, that both the quality 



