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ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 32 



this complete control of environment one can be assured of the 

 significance of growth effects arising from modifications in light 

 conditions alone. 



A first exx^eriment has been conducted by Doctor Johnston with 

 this equipment, which indicates that an excessive intensity in the 

 less refrangible end of the spectrum, that is, the infra-red and 

 extreme red, is accountable for much of the abnormal appearance of 

 plants grown in artificial light. Further experiments will be con- 

 ducted wliich will indicate to what degi'ee the long wave length end 

 of the spectrum should be excluded. In the present experiment a 

 portion of the red as well as the infra-red was cut off. Very likely 

 this will not be necessary. 



A set of color filters of unusually great diameter has been ob- 

 tained through the cooperation of the Corning Glass Works. These 

 present interesting possibilities for the investigation of the effects 

 of light upon plant growth. Figure 3 shows the transmission char- 



FiGCKE 3. — TranSDiission curves of growth chamber filters 



acteristics which we have obtained from these filters. In this dia- 

 gram transmission in per cent is plotted against wave length in 

 microns. This group offers an opportunity to study the effects of 

 different portions of the visible light, since the range of wave 

 lengths which may be supplied to the plants can be varied in con- 

 venient steps. The effects of photochemical reactions which may 

 proceed only for wave lengths shorter than some specified value may 

 be observed from the growth of plants under these various filters. 



ALGAE 



Dr. Florence Meier, National Kesearch fellow, cooperating with 

 Doctor McAlister of our laboratory, has conducted an interesting set 

 of experiments on the lethal effects of the ultra-violet upon unicel- 

 lular algae. This work has been made possible through the com- 

 pletion of a special combined spectrometer and self-recording mono- 

 chromator. The instrument is of unusually great aperture as well 

 as dispersive power. Two fused quartz prisms some 15 cm high, 

 yield a large spread of the spectrum, which makes it possible to work 

 with the relatively large slit widths required by the necessarily 



