10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



length and multiplication of numbers as observed, the volumes of the 

 cultures after exposure were proportional to the numbers in the final 

 column which are the products of the mean length by the growth 

 rate according to the cell count ratio. 



These figures indicate that the blue region produced almost as large 

 a volume as did the daylight, and one that exceeds greatly that pro- 

 duced by the other regions. The red and yellow regions also show a 

 large increase in volume, while the infrared and the green cultures 

 are less in volume than those cultures exposed to darkness. 



APrEARANCE OF THE CELLS 



The cells that had developed in the blue, yellow, and red regions 

 contained beautiful green plastids, even more green than those in the 

 daylight cultures. There were green plastids in the cells of the cul- 

 tures exposed to the green wave-length region, but a great deal of 

 granular material was also present. In the infrared cultures, the 

 plastids were green, but there were large vacuoles and much granular 

 material present in each cell. The cells grown in the darkness con- 

 tained faded yellow-green plastids that were shriveled, broken, and 

 in general presented a disintegrated appearance. 



SUMMARY 



The cell multiplication and cell length of the unicellular green alga 

 Stichococcus bacillaris Naegeli were determined after 2 weeks' growth 

 in five isolated wave-length regions of artificial light, in daylight, and 

 in darkness. 



Christiansen filters were used for the green (5000-5600 A) and 

 yellow (5500-6200 A) regions; a combined Christiansen filter and a 

 Corning heat-resisting red glass filter, " 205 percent ", provided the 

 red (6000-7500 A) ; a saturated copper sulfate solution gave the blue 

 (4000-5200 A) ; and a Corning heat -transmitting glass filter no. 254, 

 gave the infrared (8500-12000 A). The light intensity was 19.5 to 20 

 microwatts/mm 2 for each wave-length region at the beginning of 

 each experiment. 



A multiplication of algal cells of over fourfold was obtained in the 

 daylight cultures by cell counts supported by nephelometric measure- 

 ments ; over threefold in the blue, and over twofold in the yellow and 

 red regions. The green region proved to be destructive, as there was 

 a decrease in the number of cells ; the infrared region made little 

 change in cell multiplication, the cultures being very similar to those 



