XXII 



EFFECTS OF DIFFERENT REGIONS OF THE VISIBLE SPECTRUM 



UPON SEED PLANTS 



H. W. Popp AND F. Brown 

 Department of Botany, The Pennsylvania State College, State College, Pa. 



Introduction. Growth and development: Genercl studies — Effects of different regions 

 of the spectrum on fresh and dry weight of plants and on chemical composition. Miscel- 

 laneous effects of different regions of the spectrum: Effect of different parts of the spectrum 

 on transpiration — Effect of quality of light on stomata — Anthocyanin forynation in differ- 

 ent parts of the spectrum — Quality of light and absorption of inorganic salts. Reflection, 

 absorption, and trans7nission of different parts of the spectrum by leaves. Concluding 

 remarks. References. 



INTRODUCTION 



From time to time since the experiments of Tessier (48), studies have 

 been made of plants grown under colored screens. In general, the earlier 

 workers were more interested in the possible use of colored glass for 

 greenhouses than in physiological effects of radiation. Consequently 

 their experiments were comparatively crude. Often the only condition 

 mentioned in their reports was the color of the glass used. The presence 

 of radiation consisting of wave-lengths other than those of the color of 

 the glass, intensity differences, and temperature differences were often 

 ignored, yet rather extravagant claims were often made for a particular 

 color of glass. As a striking example of this may be mentioned a paper by 

 Pleasanton (32) read before the Philadelphia Society for Promoting 

 Agriculture, entitled "On the Influence of the Blue Color of the Sky in 

 Developing Animal and Vegetable Life." (Very appropriately this 

 report was reprinted on blue paper.) Pleasanton began his experiments 

 with grapes in 1861, in a greenhouse, concerning which he says: "At a 

 venture I adopted every eighth row of glass on the roof to be violet- 

 colored, alternating the rows on opposite sides of the roof, so that the sun 

 in its daily course should cast a beam of violet light on every leaf in the 

 grapery." No other conditions of radiation are given and no controls 

 were used. In this special house the author claims to have produced 

 grape vines which in five months were 45 ft. long and 1 in. thick. During 

 the second year these vines produced about 1200 lb. of grapes and during 

 the third year 2 tons, whereas grapes not so treated, according to the 

 author, normally require five to six years before any grapes at all are 

 produced. 



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