NO. 17 GROWTH OF ALGAE IN WAVE-LENGTH REGIONS MEIER 5 



The Christiansen filters used were constructed as described by 

 McAlister (1935) and are shown in plate i on the low wooden tables 

 by the lamps. The temperatures of the Christiansen filters were 

 recorded twice daily to insure control of the 3 monochromatic beams 

 utilized which were : red, yellow, and green, A Corning heat-resisting 

 red glass filter, " 205 percent ", was combined with one of the Chris- 

 tiansen filters to give the desired region in the red. Because of the 

 difficulty in obtaining a light source of sufficiently high intensity 

 that would work practically with the blue Christiansen filter, it was 



eooo 10,000 12,000 



WAVE LENOTM fANOSTROMS) 



Fig. I. — A diagram of the growth rate or cell multiplication (columns) super- 

 imposed on a diagram .showing the relative energy transmitted by each filter 

 (curves). The columns marked L and D indicate the results of daylight and 

 darkness respectively. The abscissae indicate wave lengths. On the right is a 

 scale of ordinates for the cross-hatched columns representing cell multiplication. 

 On the left is a scale of ordinates representing intensities of the radiation groups. 

 The areas under the curves representing radiation are equal, indicating the 

 equality of radiation stimuli for visible and infrared rays. For full daylight, 

 however, no measurement of the intensity of the radiation stimulus is available, 

 hence the cell multiplication in daylight is not strictly comparable to the other 

 results. 



found necessary to use a saturated solution of copper sulfate as a 

 filter. For the infrared cultures, two duplicate Corning heat-trans- 

 mitting glass filters no. 254 were used. The wave-length regions for 

 the filters are listed in the tables and shown graphically in figure i. 

 The daylight cultures were grown under natural conditions of day 

 and night in a north window of a room in the Smithsonian flag tower. 

 The dark cultures were grown in a sealed drawer of the same room. 

 Numerous experiments were essayed for over a year before the 

 three successful ones reported were completed. In experiments 2 and 

 3, the red, yellow, green, and blue colors, as described above, were 

 tested. The green and blue results checked in both experiments, but 



