RESPONSE OP PLANTS TO ARTIFICIAL LIGHT 



27 



The results with radishes were practically the 

 same. There was no fleshy root development, and 

 the plants were long and weak. There was very 

 little leaf -growth, although there was production 

 of chlorophyll. 



These experiments must be considered prelimi- 

 nary. They demonstrated that chlorophyll could be 

 formed by this light, devoid of red rays. With im- 

 provement in the electrical apparatus better results 

 are to be expected. 



Influence of colored light on plants. 



Investigations pertaining to the effects of the dif- 

 ferent rays of light on plants have been conducted 

 for many years, although many of the earlier ex- 

 periments are more or less faulty, since pure spec- 

 trum colors were not always employed, nor were 

 the plants always subjected to the same degree or 

 intensity of light. 



Flammarion found in his experiments with sen- 

 sitive plants that red light accelerated growth the 

 most, this being followed by green, white and blue 

 light, in the order named. His experiments were 

 made in a small conservatory behind clear and 

 colored glass, which, however, did not in all cases 

 furnish strictly monochromatic light. Other obser- 

 vers have shown that plants grow more vigorously 

 in orange rays and that they resemble those which 

 grow in darkness, while those subject to blue light 

 resemble plants grown in daylight. While orange 

 light produces effects similar to those in plants 

 grown in darkness, — that is, they develop small 

 leaves and elongated internodes, resembling etio- 

 lated plants, — their leaves are green. On the other 

 hand, blue light prevents the expansion of the 

 cotyledons in some cases, and, since it does not 

 induce photosynthesis, there is little need of their 

 expanding. 



The effect of orange light on the growth of 

 fungi is similar to that brought about by darkness. 

 For example, the aerial hyphse of Pilobolus become 

 greatly elongated when grown in darkness or in 

 orange light. Blue light, however, induces irritable 

 movements or heliotropic curvatures. Sachs found 

 that the elimination of the ultra-violet rays has an 

 effect on the production of flowers, causing a less 

 luxuriant development of them. The accurate ex- 

 periments of Englemann, Reinke and Timiriazeff 

 have shown that photosynthesis in green plants 

 reaches its maximum in the red and orange rays of 

 the spectrum between the lines B and C. In the 

 case of the red algse, however, the region of maxi- 

 mum assimilation is somewhat different, since the 

 greatest photosynthetic activity is shown between 

 the yellow and green bands, while in the blue-green 

 algae this occurs between the orange and yellow. 

 There is some reason to believe that such pigments 

 as phycoerythrin, found in the red algae, may pos- 

 sess some ecological significance, since the plant 

 frequently grows at considerable depths in the 

 ocean. The most active assimilation is caused in 

 the purple bacteria in the infra red rays or those 

 rays having wave lengths of 800 to 900 m ij.. 



Some investigators have noted an injurious effect 

 of the green rays on certain plants. This may be 



accounted for by unlike methods used in experi- 

 menting, although it is well known that different 

 plants respond in a different way to the same light 

 stimulus. Plants respond to the ultra-red and ultra 

 violet rays, which are well known to make no 

 impression on the retina ; and the same may be 

 held to be true in regard to other forms of radiant 

 energy. It has been shown that electrical radia- 

 tions characterized by wave lengths vastly longer 

 than the last visible red rays are able to produce 

 certain physiological effects on plants, but whether 

 this will apply to the Rontgen and Becquerel rays 

 has not been definitely proved. 



There is little likelihood of monochromatic light 

 being employed to advantage in growing crops, 

 since plants are best adapted to mixed rays, such 

 as occur in sunlight. 



Literature. 



J Reinke, Untersuchungen liber die Einwirkung 

 des Lichtes auf die Sauerstoffausscheidung der 

 Pfianzen, I. Mitt. Bot. Ztg., XVI, also, II, Mitt. Bot. 

 Ztg. XLII; T. W. Engelmann, Various papers in 

 Arch, f . d. Ges. Physiol., Vols. XXV, XXVI, XXVII, 

 XXIX, XXX ■; Cf. Bot. Ztg., Bd. XLI, XLII, XLVI ; 

 Timiriazeff, Ann. de Chim. et de physiq.. Vol. XII, 

 Comp. Rend., Vol. CX, 1890 ; J. W. Draper, On the 

 Decomposition of Carbonic-acid Gas by Plants in 

 Prismatic Spectrum, American Journal of Science, 

 XLVI ; J. W. Draper, Scientific Memoirs, 1878 ; 

 C. Flammarion, Etude de Taction des diverses 

 radiations du spectre solaire sur la vegetation, 

 Comp. Rend., CXXI, 1895. 



Some of the more important literature on artifi- 

 cial light in its relation to the growth of plants is 

 as follows: 



L. H. Bailey, Some Preliminary Studies of the 

 Influence of the Electric Arc Lamp upon Green- 

 house Plants, Bulletin No. 30, Cornell Experiment 

 Station, August, 1891 ; Second Report upon Elec- 

 tro-Horticulture, Bulletin No. 42, September, 1892; 

 Third Report upon Electro-Horticulture, Bulletin 

 No. 55, July, 1893. (Subsequent studies have 

 never been published.) G. Bonnier, Influence de la 

 lumiere ilectrique continue sur la forme et la 

 structure des Plantes, Revue general de botanique. 

 Tome VII, 1895 ; P. W. Rane, Electro-Horticulture, 

 Bulletin No. 37, West Virginia Experiment Sta- 

 tion, July, 1894 ; C. W. Siemens, On the Influence 

 of Electric light on Vegetation, and on Certain 

 Physical Principles Involved, Proceedings Royal 

 Society, XXX, 210-219 ; and Some Further Obser- 

 vations on the Influence of Electric Light on 

 Vegetation, Proceedings Royal Society, XXX, 293- 

 295, by the same author ; C. W. Siemens, On Some 

 Applications of Electric Energy to Horticultural 

 and Agricultural Purposes, Report of British Asso- 

 ciation of Advanced Science, LI, 474-480 ; P. P. 

 Deherain, Untersuchungen iiber des Einfluss d. 

 Elektrischen Lichtes auf dg,s Wachsthum d. Pfian- 

 zen, Annales Agronomiques, T. VII, 81, P. 551-575 ; 

 Wollny, Forschungen auf d. Geb. der Agricultur- 

 physik, Bd. V, p. 488; M. J. lorns. Acetylene Light 

 for Forcing Plants, Cornell Countryman, May, 1906 

 (from this article Figs. 45 and 46 are redrawn). 



