4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 92 



as Other environmental factors may bring about similar effects. This 

 demonstrates the importance of measuring or recording all these 

 factors in any study of the eft"ect of light on plants. 



Schanz (1919) grew higher plants in eight beds covered with 

 various kinds of glass. In the first five beds the range of wave lengths 

 of light transmitted was gradually decreased from the violet end of 

 the spectrum toward the red, thus making possible the study of the 

 eft'ect of light from which greater and greater regions of the spectrum 

 were eliminated in the blue-violet end. Combinations of colored 

 glasses which gave predominating colors of yellow, green, and blue- 

 violet were used in the last three beds. He found that chlorophyll 

 development in beans, soybeans, and potatoes was more rapid the 

 more the short rays were cut off, being most rapid under red light. 

 In lettuce, chlorophyll developed fully under blue-violet rays but 

 not in normal quantity in yellow or green light. Schanz did not mea- 

 sure the light intensity, nor does he give accurate information con- 

 cerning temperature and other factors that possibly varied under the 

 different types of glass. 



Popp (1926) grew a number of higher plants in greenhouses under 

 glasses transmitting only definite regions of the spectrum. The plants 

 receiving no wave lengths shorter than 5290 A or 4720 A had a good 

 development of chlorophyll and were somewhat similar to those 

 grown under reduced light intensity. There was very little difference 

 between plants that received all the rays of the spectrum of daylight 

 and those from which only ultraviolet rays were eliminated. Popp 

 claims that light intensity was not an important factor in his experi- 

 ment for the following reason : The plants grew normally and vigor- 

 ously in the full spectrum of daylight at an intensity that was at all 

 times lower than that of the house in which all wave lengths shorter 

 than 4720 A were removed and only slightly greater than that of the 

 house in which wave lengths shorter than 5290 A were eliminated. 



Sayre (1928) investigated the development of chlorophyll in seed- 

 lings under Corning glass ray filters and found that wave lengths of 

 radiant energy longer than 6800 A are not effective in the formation 

 of chlorophyll in corn, wheat, oats, barley, beans, sunflowers, and 

 radishes, but that all other regions of the remaining visible and ultra- 

 violet spectrum to 3000 A are eft'ective provided the energy value is 

 sufficient. For approximately equal energy values in these regions 

 the red rays are more effective than the green and the green than 

 the blue. The effectiveness of radiant energy seems to increase with 

 the wave length to about 6800 A, where it ends abruptly. 



