816 BIOLOGICAL EFFECTS OF RADIATION 



of various regions of the spectrum with a view to answering these ques- 

 tions. Some of the experimenters have also shown other defects, such as 

 faikire to use equal energy values for different regions of the spectrum, 

 to control temperatures, and to consider the stage of after-ripening of the 

 seeds. 



Cieslar (12) found yellow Hght most effective in forcing germination 

 of grass seeds, while violet light retarded germination. Haack (30) 

 showed that in Scotch pine yellow light was most stimulative with blue 

 far less so, but the latter better than darkness. According to Heinricher 

 (37) the less refrangible portion of the solar spectrum was favorable to 

 germination of Viscum album seeds, and the more refrangible portion 

 ineffective or injurious, with no germination occurring in darkness. 



Kinzel (46, 47, 48, 49, 50, 51) studied the action of different regions 

 of the spectrum on the germination of several seeds. Among light- 

 favored seeds he found that for Nicotiana the optimum region was yellow, 

 orange, or green; for Allium suaveolens red and white were best with green 

 and violet less favorable, but better than darkness; for Drosera capensis 

 all rays gave high germination, but the energy of germination fell in the 

 following order: white, yellow, orange, red, green, blue, violet; for 

 Pinguicula vulgaris red, white, and orange were good; green and bright 

 blue poor; yellow, dark blue, and violet intermediate; and no germination 

 occurred in darkness; for Epilobium roseum long rays of the visible 

 spectrum were better than short rays. In general, the germination of 

 light-favored seeds was favored more by the longer visible rays than by 

 the short rays. Among the light-inhibited seeds Kinzel found that for 

 Silene tartarica the blue rays of white diffuse light partly prevented 

 germination in light; for Delphinium elatum violet was the most injurious; 

 for Phacelia tanacetifolia green was better than darkness; for Asphodelus 

 ramosus yellow was the best region for germination at both 14° and 20°C., 

 violet was very injurious at 14°C., and favorable at 20°C., and red to 

 orange was toxic at 20°C.; for Nigella saliva the following rays injured 

 germination at high temperatures, the injurious effects decreasing in the 

 following order: white, bright violet, orange, red, yellow, dark blue, and 

 dark violet. 



Kommerell (54), using accurate photometric methods, studied the 

 effect of equal caloric values of different regions of the visible spectrum 

 upon the germination of the highly light-sensitive seeds of Nicotiana 

 tabacum and Lyihrum salicaria. She found the percentage germination 

 proportional to the ray length of the region falling on the surface of the 

 seed. She also determined by methods which are open to question 

 the absorption of various regions of the spectrum by the seed coats. The 

 coats of both seeds showed high absorption at 5100 A. After correcting 

 for seed-coat absorption — in doing this she disregarded various irregulari- 

 ties in the coat absorption curves — she concluded that the effectiveness 



