130 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1931 



upon exposure to light. These will be used for experiments in which 

 coloration is determined as a function of wave length and intensity. 



Provision has been made for growing a large number of algae 

 cultures under comparable conditions. For this purpose two tables 

 have been constructed, each with four glass-bottomed reservoirs. 

 Small Erlenmeyer flasks containing solution cultures of algae are 

 immersed in these large water baths and illuminated by artificial 

 light from below. A circulating system maintains each set of four 

 reservoirs at the same temperature. The small Erlenmeyer flasks 

 containing the algae are maintained in agitation by a common driv- 

 ing mechanism. Only the illumination is different in one reservoir 

 from that in another. Thus the effect of modifying wave length or 

 intensity may be determined for 18 different samples at once. The 

 flasks may be supplied with small manometers in order to make a 

 rough check on the photosynthetic processes as they are affected by 

 growth and modification of conditions of illumination. All this 

 work, however, is simply an auxiliary to the more careful experiment 

 to be carried out intensively in a modified Warburg apparatus 

 wherein differential nephelometric measurements are made as well as 

 the usual maiiometric measurements upon oxygen concentration. The 

 apparatus for these more refined measurements is in process of 

 construction. 



A large quartz spectrograph has been constructed, using two quartz 

 prisms some 15 cm on a side with quartz lenses of a 60 cm focal 

 length. By means of the spectrograph unicellular organisms distrib- 

 uted uniformly on a slide or in a culture dish may be exposed simul- 

 taneously to different regions of the spectrum. Modifications in 

 growth rate or resulting death point may be observed comparatively 

 for different wave lengths. In Plate 1, Figure 2, the results of a pre- 

 liminary exposure of algae are readily observed. For all wave 

 lengths shorter than 3,000 A the typical mercury lines appear just 

 as they would be seen on a photographic plate. Plere, however, they 

 are recorded by the absence of the organisms after a week's growth 

 subsequent to exposure. It should be noted that although the lines 

 on the long-wave length side of 3,000 A are stronger by actual ther- 

 mocouple determination they have not affected the algae colony. 



For convenience. Figure 5 may be referred to in this connection, 

 which shows the relative intensities of the different lines of the mer- 

 cury arc as determined in an experiment to be discussed later in 

 another connection. 



By a succession of such experiments, wherein the first noticeable 

 killing can be determined for different exposure times, the relative 

 dosage of different wave lengths can be determined. 



