EFFECTS OF REGIONS OF VISIBLE SPECTRUM 



767 



gveon, and bluo-violet light (beds 5 to 8) the number of flowers was 

 greatly reduced and the time of blooming postponed. 



As a general result of his work, Schanz concluded that light of short 

 wave-lengths, particularly the ultra-violet region, was detrimental to the 

 growth of plants. Hence he recommended the use of Euphos glass for 

 greenhouses. 



Schanz's work was in some respects different from that of his pred- 

 ecessors, but it is unfortunate that he made no attempt to equalize 

 intensities in the different beds and that he gave no accurate information 

 concerning temperature differences. There is consequently no way of 

 differentiating in his work between effects of quality of light and effects 

 of intensity. Furthermore, the criterion he most commonly used for 

 best growth was stature of plants, which has since then been shown to be 

 v^ery unreliable. 



In 1926, Popp (34) reported the results of his investigations, in which 

 the effect of different regions of the spectrum was studied under approxi- 

 mately equal intensities of radiation. His plants were grown in five 

 small greenhouses, each covered with a special type of glass. The 

 spectral ranges of the glasses used are given in Table 2. 



Table 2. — Spectral Limits of Glasses Used by Popp 



The intensity of radiation in house 2, which transmitted practically 

 all wave-lengths in sunlight, was reduced, by means of tobacco shading 

 cloth, to a value intermediate between the intensity of the light in houses 

 4 and 5. Thus it was possible to compare, under approximately the 

 .same total intensities, plants from which the blue-violet end of the 

 spectrum was screened out, with those receiving the full spectrum. A 

 wide variety of plants was selected, including tobacco, carrots, tomatoes, 

 buckwheat, Sudan grass, soy beans, sunflowers, petunias, and 

 four-o'clocks. 



Most striking results were obtained in house 5, in which all wave- 

 lengths shorter than 5290 A were eliminated. The plants in this house as 

 compared with those of house 2 receiving the full spectrum, all showed a 

 more rapid rate of elongation during the first two to three weeks of growth. 

 Soy beans, tomatoes, four-o'clocks and Coleus attained the greatest final 



