672 Arber . — On the Effect of Nitrates on the 
There was also a marked difference in the condition of the 
Alga. After six days in the KN 0 3 solutions, the seaweed 
was not far from the point of death, while the Algae in the 
NaCl solutions were quite healthy. The object of these 
experiments with distilled water, as in the case of the other 
nitrates, was to see whether Ulva could assimilate in solutions 
of this salt alone, as it was found to do in the case of sodium 
chloride. I concluded that this was not the case. The results 
of Experiments I and II show that the absence of assimilation 
was not due so much to the absence of certain necessary salts, 
as to a detrimental effect caused by the presence of the nitrate. 
With a view to testing this point, I made experiments (as also 
with other nitrates) in which certain percentages of potassium 
nitrate were added to sea water , on the assumption that if this 
salt was not harmful to the plant the carbon-assimilation 
would be normal. A series of solutions were made consisting 
of sea water to which -5 per cent., 1 per cent., and 2 per cent. 
KN 0 3 was added; and in these Ulva was exposed to light. 
I never obtained from Algae in solutions containing *5 per 
cent. KN 0 3 more than a ‘little’ starch, from those in 1 per 
cent. KN 0 3 mor e than a ‘trace,’ and in 2 per cent. KNO s 
solutions no starch whatever was found. I therefore con- 
cluded that the presence of an appreciable amount of KN 0 3 
in the sea water caused an inhibition of the C 0 2 -assimilation. 
(B) Sodium Nitrate. 
As with other nitrates, the proportions of sodium nitrate 
used were those equivalent to o-i, 0-5, 1, 2, &c. per cent. 
KN 0 3 , the latter being taken as a standard in all cases. 
1 gram KNO s is equivalent to *8415 gram NaN 0 3 . The 
following experiment is typical of the effect of this nitrate in 
sea water : — 
Experiment V. June 7, 1900. Sea water + NaN 0 3 . 
Date. 
Days . 
Equivalent 
to 1 % KNO z . 
Equivalent 
t 0 O'$%KN0s. 
Control sea-water 
alone. 
June 12 
5 
moderate 
not quite 
moderate 
moderate 
June 14 
7 
moderate 
moderate 
maximum 
