EFFECTS OF REGIONS OF VISIBLE SPECTRUM 765 



tures. Hence the shape and growth of a well-nourished plant remain the 

 same behind a solution of cupric oxide in ammonia as in somewhat weak- 

 ened white light, whereas behind a solution of potassium bichromate, 

 which allows the red and yellow rays to pass, but cuts off the blue and 

 ultra-violet ones, flowering plants turn green, but otherwise grow as 

 though in darkness or in very feeble light." 



While it was recognized by Pfeffer and many others that the red end 

 of the spectrum had an etiolating effect on plants, many of the earlier 

 workers interpreted the greater height or stem length of the plants under 

 these conditions as a favorable growth effect and therefore stated that 

 the best plants were produced under red light. Thus, throughout Flam- 

 marion's (12) work of over 15 years, he repeatedly reports best growth 

 under red light, although he himself found that the weight of plants was 

 usually greater under clear glass than under any other type. Flam- 

 marion grew plants in hothouses under red, green, blue, and clear glass, 

 respectively. Of these, the red glass was the most nearly monochromatic. 

 The hothouses were ventilated so as to overcome wide differences in 

 temperature. Even when an attempt was made to equalize intensities 

 under red and under clear glass, red light produced rnuch taller plants, 

 but with thinner stems and much lower in weight. Blue light always 

 resulted in weak, undeveloped plants of very low weight, probably because 

 of the low quantity of radiant energy transmitted. Flammarion used 

 many kinds of plants and studied also effects of different colors of light 

 on flowering, fruiting, coloration, transpiration, and to some extent on 

 composition. 



Corbett (7) supplementing daylight with green, blue, and red light in a 

 greenhouse at night, obtained a marked stimulating effect of red light on 

 lettuce. Green and blue lights were not stimulating. It is not possible 

 in this work to separate photoperiodic effects from quality effects of light. 

 Teodoresco (46), Kraus (22), Vines (52), Hood (17), Zacharewicz (55), 

 Villon (51) and others conducted experiments with colored light in this 

 early period. Without going further into the details of their work, some 

 of which was very extensive, it is important to note that none of it could 

 be absolutely relied upon as regards effect of quality of light on growth 

 because of the constant differences in total radiation intensity, duration 

 of light, temperature, and other factors that were not taken into account. 



In 1918 Schanz (37) reported the first of a series of experiments in 

 which he studied the effect on plants of withholding from them definite 

 regions of the spectrum in the blue-violet end. In this paper he tried to 

 prove particularly that ultra-violet radiation influences the configuration 

 of plants in general, by checking their growth. This conclusion was 

 reached by comparing the height of plants in high altitudes with that of 

 the same species growing in lowlands, and also by growing plants in 

 beds covered with window glass, Euphos glass, and red glass, respectively, 



