422 



Plant Physiology 



cent, the harmful rays are largely excluded. Continuous 

 night illumination with the electric arc may promote more 



rapid growth in some 

 plants, but with others 

 there is a tendency to 

 run to seed. 



The incandescent elec- 

 tric light, which is rela- 

 tively rich in red rays, 

 has been successfully em- 

 ployed by Rane in forc- 

 ing lettuce. By the use 

 of the acetylene light 

 Craig has found it possible 

 to force the growth of 

 radish, lettuce, and a few 

 other crops ; but the best 

 results were with flowers, 

 Easter lilies especially giv- 

 ing increased production 

 in a shorter time. 



257. Monochromatic 



FIG. 116. Field peas grown for equal 



periods in white (a), blue (6), and ments have been made to 

 orange-yellow (c), light. determine approximately 



the effects of light of different wave lengths on the form 

 and structure of plants. In much of the work which 

 has been done pure screens were not employed, yet his 

 type of work is sufficiently important to justify careful 

 physical methods. In general, the dry weight of plants 

 grown for a considerable period under monochromatic 



