380 S. O. MAST 



colonies adapted to the various colors could readily and accu- 

 rately be compared with each other and with those of the colonies 

 adapted to darkness or to strong diffuse light. 



Without going into details regarding the results obtained, it 

 may be said that in practically every test the red- or yellow- 

 adapted colonies responded essentially like dark-adapted colonies 

 and the blue- or green-adapted ones responded essentially like 

 light-adapted colonies. The red- and yellow-adapted colonies 

 were usually negative in strong and positive in weak illumination, 

 never the reverse; while the green- or blue-adapted colonies, like 

 light-adapted ones, were frequently positive in strong and 

 negative in weak illuminations.- 



The colors to which these colonies w^ere adapted were not 

 spectroscopically tested and the illumination was not measured. 

 The question, consequently, arises as to whether or not, under 

 the conditions of the experiments, photosynthesis in the red and 

 the yellow was actually greater than in the blue and the green. 

 This question was answered as follows : 



A given amount of pond-water taken from a vessel containing 

 colonies equally distributed was put into each of six 100-cc. wide- 

 mouthed bottles. One of these bottles was now placed in each 

 of the four boxes mentioned above, i.e., in the red, the yellow, 

 the green, and the blue light used in the preceding experiments; 

 one was put into darkness and the remaining one into strong 

 diffuse" light. After having been in these illuminations one or 

 more days a given amount of solution was removed from each 

 bottle and put into a test-tube. A drop of neutral red was now 

 added to the solution in each tube. This solution was found to 

 be distinctly akaline in every case. Hydrochloric acid was then 

 added to each tube until all were practically neutral and the 

 same in color. The solution in the tube which required the 

 greatest amount of hydrochloric acid was, of course, the most 

 strongly alkaline, and in this solution photosynthesis had been 

 most rapid, for carbon dioxid is consumed in the process of pho- 

 tosynthesis and the alkalinity is dependent upon the amount of 

 carbon dioxid present. 



