SMITHSONIAN MISCELLANEOUS COLLECTIONS 



94 



by the senior author had given an approximate range of 5200 to 

 7000 A for the promoting effect, with a sharp faUing off in germina- 

 tion in the long red. No inhibitory effect had been suspected as as- 

 sociated with this falHng off, however, until the effort was made to 



Fig. 2. — Energy transmission curves of green Wratten filters. The ordinates 

 are relative energies transmitted at each wave length (indicated as abscissae). 

 Numbers 56 and 60 are typical of the green filters transmitting light that in- 

 hibits germination. Numbers 64 and 67 transmit light that promotes germination. 



explain the physical basis for tha promoting effect of the light trans- 

 mitted by the two aberrant green filters. The spectrum set-up previ- 

 ously used by the senior author had been considerably modified in these 

 cooperative studies to permit a more precise measurement of the wave 



