370 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



Since plants have been growing on the earth for millions of years 

 it is reasonable to assume that their physiology is adjusted best to 

 sunlight. Although there is experimental evidence to show that 

 different processes go on better in some wave lengths than others, yet 

 the exact relationship of each to radiation should be studied sej)- 

 arately under Avell-isolated portions of the spectrum. This creates 

 another problem for the physiologist. Numerous color filters have 

 been made whereby sections of the spectrum are isolated, but with 

 all these filters the regions are not sufficiently narrow for an accurate 

 analysis of the problems. Furthermore, many filters are transparent 

 to wave lengths other than the ones desired, thus making it difficult 

 to interpret the results. Considerable progress has been made in 

 obtaining filters, and some of the difficulties have been removed by 

 the adaptation of the Christiansen filter with its improvements as 

 developed in our laboratory by Dr. McAlister (1935). This is the 

 filter that Mr. Hoover used in his studies on the photosynthesis of 

 Avheat in different wave lengths of light. 



I Avish to call your attention to another possible method of obtain- 

 ing isolated wave lengths for experimental purposes. Different 

 metallic elements when electrically excited emit light of characteristic 

 wave lengths. This is familiar to all of us in the neon and mercury 

 lights so common at present. For our experimental work with plants 

 it becomes a problem to select the proper elements that will give 

 light of a desired wave length and intensity. One light for which 

 we have a specific need is that given out by the element cadmium. 

 Leland B. Clark, of the Smithsonian Institution, is at present experi- 

 menting with the manufacture of this lamp. 



With better light filters and with the construction of new light 

 sources it is hoped to break white light into narrower and narrower 

 spectral regions of sufficient intensity to study more accurately the 

 many reactions that take place in the living plant — reactions upon 

 which life itself depends, 



REFERENCES CITED 

 Abthub, John M. 



1932. Red pigment production in apples by means of artificial light sources. 

 Contr. Boyce Thompson Inst., vol. 4, no. 1, pp. 1-18. 

 Douglass, A. B. 



1932. Tree rings and their relation to solar variations and chronology. In 

 Research Corporation Awards to A. E. Douglass and Ernst Antevs 

 for Researches in Chronology. Smithsonian Ann. Rep. 1931, pp. 

 303-324. 

 DUGGAB, Benjamin M. 



1936. Biological effects of radiation. (2 vols.) New York. 

 Flint, Lewis H. 



1936. The action of radiation of specific wave lengths in relation to the 

 germination of light-sensitive lettuce seed. Compt. Rend. Assoc. 

 Internat. Ess. Sem., Copenhagen, no. 1. 



