104 STUDIES OF PHOTO-SYNTHESIS 



the open flask. May 14. Growth in the stoppered flask has 

 stopped, no gas bubbles are given off in sunlight, but there is a brisk 

 effervescence in the open flask, and the growth is obviously in- 

 creasing. May 20. All growth is stopped in the closed flask, and 

 the growth has turned brown and flocculent. But the growth in the 

 open flask is healthy and increasing, and gives off bubbles in sunlight. 

 Frequent observations were taken till the conclusion on August 5, 

 but for brevity these may be omitted. The growth in the open 

 flask remained green and healthy to the end. No fresh growth 

 started in the stoppered one, and at the end it had only a very few 

 brown flocculi from the initial effort, ere its small store of dissolved 

 carbon dioxide and nitrogen became exhausted. The contrast at 

 the end between the two flasks was most marked. 



Frequent examination with the microscope, through the wall of 

 the flask, of the growing clumps of green organisms, showed the 

 presence of only two type? of round- celled unicellular algae. One of 

 these was smaller than the other and of a brighter green, and was 

 identified as chlorella; the other was of about twice the diameter, 

 not so regularly spherical, and of a brownish- green colour. There 

 were no diatoms or other motile green organisms. No mycelium 

 or other evidence of fungi were seen, and the absence of any turbidity 

 at the end showed there was no appreciable development of bacteria. 

 Drops examined at the end showed no bacterial growths. 



Blank experiments on the water used showed that it contained 

 about 1 mgrm. per litre of amino-nitrogen, and about 0-3 mgrm. 

 per litre of nitrogen as nitrite and nitrate. In addition to this 

 control, there is the control of the stoppered flask contents. 



The contents of the two flasks were analysed on August 5. The 

 water in each, slightly acidified with sulphuric acid to prevent any 

 loss of amino-nitrogen, was evaporated down almost to dryness; 

 then in each case the growth was added ; destruction with sulphuric 

 acid followed, and the nitrogen determination was made by the 

 ordinary Kjeldahl process. 



The results were that the open flask contained 5-00 mgrms. of 

 nitrogen, while the stoppered flask contained only 1-95 mgrms. 

 A third flask of transparent silica, containing the same water, which 

 had been exposed during the entire period of the experiment to such 

 bright and direct sunlight as was available, developed no growth 

 whatever, probably because the cells were destroyed by the intenser 

 light and shorter wave-lengths. The water in this flask was 



