NO. 5 IRRADIATED LETTUCE SEED FLIXT AND McALISTER 3 



as those of Gardner (4), Lehmann (7), Maier (8), Nathammer (10) 

 and Shuck (11), have concerned themselves for the most part with 

 white hght as a quantitative factor in germination. 



Wholly unaware of the foregoing background of researches by- 

 German workers in this field, the senior author discovered that so- 

 called " dormant " lettuce seed would germinate readily in white light, 

 and further, that yellow, orange, or red light promoted this germina- 

 tion, whereas violet, blue, or green light inhibited it. It now appears 

 that the germination response to radiation of specific wave lengths 

 noted for dormant lettuce seed represents types of reactions of wide 

 occurrence among seeds. This fact suggests that the further study 

 of such responses may be warranted as promising results of both prac- 

 tical and theoretical significance in relation to germination and pos- 

 sibly also in relation to other aspects of growth. The results obtained 

 by Flint (3) with green Wratten filters indicated that color alone was 

 not a safe criterion to use in the interpretation of results obtained with 

 filters, thus directing attention to their wave-length transmission. 



METHODS 

 The principal line of attack in this investigation involved the use 

 of a spectrum, and to a large extent the work comprised successive im- 

 provements in the technique of utilizing the spectrum to the greatest 



Fig. I. — Schematic drawing of the apparatus used in the study of spectral ligl 

 in relation to germination. 



advantage in relation to germination. The set-up as finally elaborated 

 (see fig. i) consisted of a fixed light source, a condenser lens con- 

 centrating light upon an adjustable slit, an achromatic lens, a prism, 

 and a silvered mirror. A light-proof house surrounded the set-up, 

 with a partition at the slit (not shown in the figure). With this set-up, 

 using a single filament 1,000 lumen 6.6 ampere Mazda street-lighting 

 bulb as a light source, a spectrum was obtained which was about i foot 

 long in the visible range. 



