676 Arber . — On the Effect of Nitrates on the 
absorbed, a larger amount of free acid would be set free by 
the decomposition. As such Algae as Ulva are well known 
to be extremely sensitive to acid solutions, which are generally 
injurious to such plants, the inhibition of the C0 2 -assimilation 
may be due to a greater amount of acid than usual being set 
free. The varied degree of inhibition, which different nitrates 
were found to cause, may conceivably be explained by the 
metal of certain nitrates having a greater affinity for the 
organic acid radical. The potassium and ammonium of 
KN0 3 , and NH 4 N0 3 , may be more eager to unite with 
the oxalic or other organic acid than the sodium or mag- 
nesium of NaN0 3 , and Mg(N0 3 ) 2 , and thus cause a greater 
inhibition. It was pointed out in a former paper that 
certain sulphates, especially calcium sulphate, were found 
to be similarly injurious. Possibly this effect may be ex- 
plained in the same way, for Schimper 1 has shown that the 
fate of both nitrates and sulphates is closely analogous, in 
that they are both reduced. The type of reaction in these 
cases is — 
C 6 H 12 0g + 2 HNO 3 = c 4 h 8 n 2 o 3 + c 2 h 2 o 4 + 2 H 2 o + 30 
Sugar Asparagin Oxalic acid 
Schimper has also pointed out that, while potassium oxalate 
is exceedingly common in plants as the first stage in the 
formation of calcium oxalate, the presence of sodium oxalate 
is exceedingly rare. This fact may possibly have some bear^ 
ing on the assumption suggested here, that the difference in 
effects caused by potassium and sodium nitrates, is due to 
a difference of chemical affinity on the part of the metallic 
radical. 
Potassium Phosphate . 
With a view to supporting the explanation here suggested 
to account for the effect of nitrates on Ulva, some similar 
experiments were made with potassium 'phosphate. The 
phosphates which could be used for this purpose are very 
1 Schimper (’90). 
