IN FRESH- WATER ALGJE 111 



nitrates or other easily assimilable nitrogen, and this has greatly 

 repressed the production of growth. The two amounts of nitrogen 

 of 1-0 and 1-1 mgrrn. are, however, considerably above the controls 

 namely, 0-1 to 0-3 so that it would appear probable that there was 

 a slow fixation of atmospheric elemental nitrogen. (See in this con- 

 nection the next experiments, Nos. 3 and 4, and the succeeding 

 chapter on Marine Algae.) 



Experiment 111. Commenced August 9, 1918 ; terminated August 

 29, 1918. This set was likewise carried out in Kilner jars, and was 

 designed to test whether, with exclusion of the free atmosphere, 

 nutrition and growth could be achieved by feeding with high 

 dilutions of carbon dioxide, and of oxides of nitrogen. The experi- 

 ment was carried out as follows : 



Eight Kilner jars were taken. Each of these received 100 c.c. 

 tap water, 1 c.c. of a 1 per cent, solution of sodium chloride, 1 c.c. 

 of a 1 per cent, solution of alkaline potassium phosphate (K HP0 4 ), 

 and two drops of a 1 per cent, solution of ferric chloride (equivalent 

 to 0-14 c.c.). Then to each was given a minute insemination of 

 1 c.c. of a dilute suspension of a unicellular green algal growth. 

 The eight jars were set out on the lawn in the daylight on August 9, 

 each being loosely covered by its lid, but opened daily, so as to 

 establish growth in each case preparatory to the subsequent treat- 

 ment. On August 16 growths were evident, and about equally 

 advanced in all the jars; numerous fresh colonies had started 

 attached to the bottoms, and in the precipitated calcium phosphate. 

 The eight jars were now divided into four pairs. The first pair 

 (Nos. 1 and 2) simply had their lids screwed on airtight. The second 

 pair (Nos. 3 and 4) first had a narrow test-tube, similar to that 

 described in Experiment II., and half filled with solid sodium bicar- 

 bonate inserted, and both then had their lids screwed on airtight. 

 The third pair (Nos. 5 and 6), instead of the sodium bicarbonate tube, 

 had a similar tube, containing a system* designed to evolve nitrogen 

 peroxide and other oxides of nitrogen very slowly into the air of the 

 jar. The fourth pair (Nos. 7 and 8) each had two tubes, one con- 

 taining sodium bicarbonate, and the other the nitrous system. 

 This nitrous system was constructed thus : A few crystals of sodium 

 nitrite were introduced into the narrow test-tube, the tube was then 

 gently half filled with water, and on top of this there was introduced 

 a column of about 3 cm. of 1 in 10 nitric acid. 



The design of the experiment was to shut off all atmospheric 



