674 Arber. — On the Effect of Nitrates on the 
*5 per cent. KN0 3 , no starch whatever was obtained even in 
a week, or at the most the slightest ‘ trace.’ The control was 
the same as in experiments with KN0 3 . The Alga became 
unhealthy, and died in a very short time. 
Such conclusions as may, I think, be drawn from these 
experiments, but which, in some cases, can only be regarded 
as provisional, are as follows. No solution, containing a 
moderate percentage of these nitrates alone ^ is at all com- 
parable to one of an equivalent percentage of NaCl, as 
a medium for normal C0 2 -assimilation. The effect of the 
presence of 1 per cent. KN0 3 , or its equivalent of the other 
nitrates experimented with, is in all cases to lower the amount 
of C0 2 -assimilation as judged by the amount of starch found 
in the thallus. With magnesium nitrate this is least marked, 
and next sodium nitrate. Potassium nitrate has a very in- 
jurious effect, while ammonium nitrate is absolutely fatal. 
These results are remarkably in accordance with those of 
Loew and Bokorny in regard to Spirogyra , and also with the 
conclusions of Stange as to the prejudicial effect of KNO a on 
many fresh-water Algae. In the case of Ulva , NaN0 3 was 
also found to be less injurious than KN0 3 , and the ammonium 
salt equally fatal, but in the former case there was no sign of 
any abnormal amount of starch being formed. 
These results were, in the main, confirmed at the Bradford 
meeting of the British Association, where I gave a brief 
sketch 1 of the chief conclusions to which I had attained. In 
a paper which followed, by Messrs. Letts and Hawthorne 2 , 
on the relation of this Alga to the pollution of sea water by 
sewage, it was stated that no carbohydrates beyond cellulose 
could be found, on analysis, in specimens growing in the 
polluted sea water. Dr. Letts said at the time that he was 
much struck by the absence of all traces of carbohydrates 
such as starch. These authors have made out a very good 
case to show that Ulva can, under some circumstances, derive 
its entire nourishment from organic materials, especially from 
substances rich in combined nitrogen, and without carbon- 
1 Arber (’00), p. 934. 2 Letts and Hawthorne (’00), p. 935. 
