122 STUDIES OF PHOTO-SYNTHESIS IN MARINE ALG^E 



in fats, to a fixation of 130 mgrms. of carbohydrate, 100 mgrms. of 

 protein, or 80 mgrms. of fats. 



Turning now to the increased moist weight during the experiment 

 from 2-00 grms. to 2-57 grms. and taking the dry weight at the end as 

 0476 grm., the increase in dried weight works out at 106 mgrms. 



2-00 

 (the initial dry weight being calculated as 0-476 x s~H7 rm -) - 



There is thus a close correspondence between the increase in 

 weight and that which would be expected viz., increase in 

 dried weight found, 106 mgrms. ; expected increase in dried weight if 

 all were converted into carbohydrate, 130 mgrms. ; expected increase 

 if all protein, 100 mgrms. ; expected increase if all fat, 80 mgrms. 



If next the increase in the nitrogen be considered, this amounts 

 to about 3 mgrms., which corresponds to about 20 mgrms. of protein ; 

 the remaining 80 to 90 mgrms. fixed would therefore represent the 

 carbohydrates and fats. 



ADDENDUM ON NITROGEN-FIXING BACTERIA. 



Our attention has been drawn to the fact that three different 

 observers 1 have demonstrated that the surface of the ordinary large 

 seaweeds is regularly colonised by nitrogen-fixing bacteria, and it 

 has been stated that these bacteria have been identified with the 

 nitrogen-fixing bacteria known in soils. 



Reinke states that nitrogen bacteria were found without ex- 

 ception on all the marine algae of Heligoland sent to the Botanical 

 Institute at Kiel for examination. The thoroughly washed alga 

 was placed in a suitable nutritive medium, and there followed a 

 heavy development of azotobacter and corresponding fixing of 

 nitrogen from the air. 



In Keutner's experiments small pieces of various algso were in- 

 troduced into a culture medium, and in about ten days the fluid 

 became turbid and a scum was formed on the surface of the water 

 and on the pieces of seaweed. The bacteria could be identified 

 in the slime on the algae. Experiments made on fresh- water plants 

 gave the same results. This observer definitely states that the 

 culture flasks were kept either in a closed chest or cupboard or in a 

 thermostat -that is to say, in the dark. 



1 Reinke, Ber. deut. bot. Gesell., vol. xxii., p. 95 (1904); Keutner, Wissen. 

 Meeresuntersuch., Kiel, vol. viii., p. 27 (1905); Keding,?7?V., vol. ix., p. 275. 



