EFFECTS OF REGIONS OF VISIBLE SPECTRUM 771 



Boyce Thompson Institute. Arthur el al. (2) in some of their experiments 

 increased the intensity of the bhie-violet end of the spectrum by using 

 carbon arcs or mercury-vapor arcs in combination with Mazda lamps. 

 Such a combination gives a type of radiation more nearly Uke the quaUty 

 of dayhght. 



EFFECTS OF DIFFERENT REGIONS OF THE SPECTRUM ON FRESH 

 AND DRY WEIGHT OF PLANTS AND ON CHEMICAL COMPOSITION 



In the previous section on growth and development, little was said 

 concerning fresh and dry weight of plants because many of the investi- 

 gators did not use such data as a basis for measuring growth. In the 

 final analysis, weight increase is often a better measure of growth than 

 is height. Very often, when the earlier investigators did furnish data 

 on weight and composition, the results could not be depended upon 

 because of poorly controlled conditions. It may, none the less, be 

 interesting to note some of their results and to compare them with later 

 work. 



Flammarion (12) in his studies did observe that, although plants 

 grown under red light were taller, they were always lower in weight 

 than those grown under clear glass. His plants grown under blue glass 

 were always not only stunted, but also much lower in weight. Here, 

 however, the principal cause was probably greatly reduced intensity. 

 Lubimenko (24), on the other hand, found that the blue and violet rays 

 were more favorable to the accumulation of dry substance than the red 

 ones. This is in accord with the later and more accurately controlled 

 experiments of Popp (34) and Shirley (43) which will be considered 

 presently. 



Among the other workers who have emphasized weight and com- 

 position may be mentioned the following: Dumont (10, 11), Bassalik (3), 

 Canals (6), and Hosterman (18). Dumont covered equal areas of wheat 

 already in full flower with frames containing black, clear, red, green, and 

 blue glasses, respectively. The plants were kept covered until the 

 grain ripened. Determinations of various nitrogenous substances in 

 the grain and the heads indicated that those ripened under the red glass 

 were lowest in nitrogen content. The author concluded that the more 

 refrangible rays of the visible spectrum promoted translocation of 

 nitrogenous materials to the ripening grain and favored the formation 

 of albuminoids. Bassalik found a higher content of oxalic acid in 

 Rumex acetosa in red light than in blue light, but both red and blue 

 gave lower values than white light. Canals found that the essential 

 oil, thymol, was more abundant in Thymus vulgaris grown under blue 

 glass than under red glass, but not so abundant as that grown under 

 white glass or in the open air. Hosterman reported increased numbers 

 and weight of cucumbers grown in sunlight supplemented by the red 



