IN FRESH- WATER ALG.E 103 



subject from this aspect, we have examined the simplest unicellular 

 algse, and have found that they do possess this dual function. 



In order to obtain as pure air as possible, the exposures and 

 growths were made in the open air at Heron's Lodge, Heronsgate, 

 Chorley Wood, Herts. The house is about 1 J miles from the railway 

 line, stands on high ground at an elevation of about 400 feet, and 

 possesses a large lawn, in the middle of which all the experiments, 

 except the first, were made. The air was tested daily for nitrites by 

 starch and potassium iodide papers, and nitrites were nearly always 

 present. At the conclusion of the experiments, the growths and 

 waters were taken to the laboratory and analysed for content of 

 nitrogen by the Kjeldahl method, when an unmistakable amount 

 of fixation was found. The experiments were made in the spring 

 and summer of 1918, in the months of April to August inclusive. 



Experiment I. Commenced April 15, finished August 5. Two 

 clear glass flasks of Jena glass, each of 1000 c.c. capacity, were 

 taken, and provided with ground-glass stoppers. These were almost 

 completely filled with water from a clear stream near the house. One 

 was filled up to the glass stopper, and then the stopper was inserted, 

 so that the contents of the flask were completely shut off from the 

 air. The other flask was filled so that the water stood in its neck 

 about 4 cm. from the top; the glass stopper was not inserted, but 

 instead a loose plug of cotton- wool was used. Over this a piece of 

 fine muslin was placed and tied round the neck of the flask with 

 thread; air, accordingly, had access to the contents of this flask. 

 The glass- stoppered flask is a control to give the amount of nitrogen 

 present at the outset plus any that can possibly be formed in absence 

 of air. 



The two flasks were placed outside on the ledge of a first-floor 

 window, facing almost due west, so that direct sunlight was only 

 obtained for a few hours in the afternoon. Care was taken to give 

 equal chances to the two flasks by reversing their positions on the 

 ledge every two or three days. Also a small beaker was inverted 

 over the cotton-wool, to prevent contamination by rain. The 

 flasks were not inseminated with any organism, but left to develop 

 their crops naturally. 



On May 2 a distinct green growth appeared in both flasks,, 

 slightly greater in the glass- stoppered one. On May 7 the open 

 flask showed a distinctly greater growth than the stoppered one. In 

 dire.ct sunlight bubbles of gas aje evolved from bath, but most frora 



