NO. 5 IRRADIATED LETTUCE SEED FLINT AND McALISTER 5 



and the seeds in each compartment were transferred immediately to 

 numbered petri dishes, placed in a refrigerator at 3° C, and exposed 

 to blue light (to prevent further germination), where they were kept 

 until germination counts could be made. 



In plotting the germination percentages against radiation the wave 

 length falling on the median line of each compartment was taken as 

 the wave length for the seeds of that compartment. 



In plotting the inhibitory influence in the violet-blue-green region 

 as corrected for energies involved, the curves were inverted to facili- 

 tate subsequent comparison with other data. 



The transmission curves of the Wratten filters and of the ether 

 extracts of lettuce seeds were made in the conventional manner with 

 a double monochromator and a thermocouple. 



RESULTS 



In the experiments of Flint (3) two green Wratten filters were 

 found to transmit light that promoted germination, and 10 green 

 Wratten filters were found to transmit light that inhibited germina- 

 tion. The spectral transmission of all the green Wratten filters was 

 studied, and the energy transmission curves were obtained by mul- 

 tiplying the percentage transmission by the energy radiated from a 

 Mazda lamp at each wave length. The energy radiated by the lamp at 

 each wave length was obtained from its known spectral energy curve. 

 These energy values were used in conjunction with the inverse square 

 law and the distances at which the respective filters (when used with 

 the Mazda lamp) gave equal response with a Weston photronic cell. 

 The energies transmitted by representative green Wratten filters are 

 shown in figure 2. 



It is to be noted from the curves of figure 2 that the two green 

 filters which had been found to transmit light promoting germination 

 (64 and 67) transmitted more of the ultraviolet and less of the long 

 visible red than the green filters which had been found to transmit 

 light inhibiting germination (56 and 60). This fact suggested that 

 the promotion was associated either with a promoting influence in the 

 ultraviolet or with an inhibiting influence in the long red or near 

 infrared. 



A substantial series of exposures of moist dormant lettuce seed 

 to various wave lengths in the ultraviolet ranging from the lower 

 limits of the visible spectrum to below the ultraviolet characterizing 

 solar radiation gave uniformly negative results, whereupon attention 

 was directed to the infrared regions. Earlier studies with a spectrum 



