EFFECT OF LIGHT ON THE GERMINATION 



OF SEEDS 



E. H. TOOLE 



Agricultural Research Service, U. S. Department of Agriculture, 



Beltsville, Maryland 



The effect of light on the germination of seeds has been discussed for 

 nearly a hundred years, but it was the work of Flint and McAlister in 

 1937 that first demonstrated a clear-cut promotion of germination by 

 red Hght and an inhibition by far-red radiation. Reviews of much of 

 the voluminous literature on the role of light in seed germination have 

 been given by Crocker (1936), Evenari (1956), and Toole et al. 

 (1956^). 



The work of our group started with the results of Flint and Mc- 

 Alister as a background. The two-prism (glass) spectrograph pre- 

 viously described by Parker et al. (1946) permitted the determination 

 of quantitative action spectra for the germination of seeds of Grand 

 Rapids lettuce {Lactuca sativa L.) (Borthwick et al., 1952) and of 

 Lepidium virginicum L. (Toole et al., 1955a). The results (Fig. 1) 

 are expressed as relative incident energies at different wavelengths 

 required to promote or to inhibit germination to half its maximum 

 value. The regions of the spectrum effective for promotion and for 

 inhibition are not far separated; in fact, an overlapping of effects 

 actually occurs at about 7000 A. The activity of the blue end of the 

 spectrum (4100-5200 A) was tested, but the response in this region 

 was very low. 



A similar response to these two regions of the spectrum has also 

 been demonstrated in our laboratory for seeds of the following 

 species: Barbarea vulgaris R. Br., Berteroa iiicana (L.) DC, Brassica 

 nigra (L.) Koch., Camelina microcarpa Andrz., Capsella bursa- 

 pastoris (L.) Medic, Lamium amplexicaiile L., Lepidium densiflorum 

 Schrad., Lycopersicum esculent um Mill., Lythrum salicaria L., Nicoti- 

 ana tabacum L., Oenothera biennis L., Pinus virginiana Mill., Sisym- 



89 



