SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. 95 



grating was not of the highest quality, but precautions against spurious 

 effects from scattered Hght were taken by employing filters of colored 

 cellophane. 



Although the idea of forces arising from a wave-length gradient 

 may appear strange, they are to be predicted under certain conditions. 

 There are many varied functions performed in and by various parts 

 of the plant. In respiratory processes, carbohydrates, fats, and pro- 

 teins, water and minerals are mobilized and oxidized. In synthesis, 

 in addition to the simple process of carbohydrate formation, there are 

 reactions with ammonia or other nitrogen compounds, and further 

 condensation and polymerization of the synthesized products. Also 



5000 



6000 



7000 



8000 



Fig. I. — The percentage of germination (ordinates) of light-sensitive lett 



seed in different wave-length regions (abscissae) of the spectrum aft 

 posure to red light sufficient to effect a 50 percent germination. (F 

 and McAlister.) 



uce 



:er an ex- 



From Flint 



the processes of transportation and storage are involved. Many differ- 

 ent enzymes, catalysts, and hormones must be involved. Some of the 

 processes other than the simple carbohydrate synthesis that is ordi- 

 narily thought of in connection with photosynthesis must involve ex- 

 ternal energy obtainable by thermal contact or from radiant energy of 

 effective wave length. 



Recently the effect on the germination of lettuce seed of radiant 

 energy of various frequencies has been determined by Flint and 

 McAlister (2). They found regions of inhibition and of activation 

 in the spectrum of the light of the incandescent tungsten filament. 

 The significant point is that the boundary between promoting and 

 inhibiting regions is very sharp. (See figure i.) If a light source had 



