66 Arber.—On the Effect of Salts on the Assimilation 
starch. In experiments with i or 2 per cent. Mg S0 4 I failed 
to get a larger amount of starch. I therefore concluded 
that Mg S0 4 was a salt less favourable to carbon-assimilation 
than Na Cl. 
(C) Na 2 S0 4 . 
Glauber’s salt does not occur in sea water, but two experi- 
ments were tried in the hope that a larger amount of starch 
would be obtained than in the case of the other sulphates. 
A 2 per cent, solution was used, and gave similar results ; 
after 3 days a f trace,’ after 7 days a ‘ little.’ 
The general conclusion of these experiments with sulphates 
alone was similar to those obtained with chlorides other 
than NaCl. The amount of starch was never greater than 
a ‘ little,’ often only a ‘ trace,’ a result which would have been 
obtained by using distilled water alone. The experiments 
with Ca S0 4 seemed to give even a worse result. 
Section XIII. Conclusions. 
There has been a tendency in recent work to call greater 
attention to the importance of the absorption of inorganic 
salts for the maintenance of carbon-assimilation. Stahl 1 
in particular has adopted this standpoint in regard to the 
theory of the biology of nyctitropism. 
From my experiments it seems clear that in the case of 
Ulva a marked inhibition of the power of carbon-assimilation 
can be caused by the absence of suitable or necessary inor- 
ganic salts, and especially by an almost complete absence 
of sodium chloride. The absence of a certain salt from the 
medium may cause an inhibition just as much as the presence 
of an unfavourable salt in the medium. In Ulva, and probably 
in other plants of similar structure and habitat, sodium 
chloride was found to have a peculiar value in regard to 
carbon-assimilation, and although a full measure of carbon- 
assimilation is doubtless only reached when the whole or 
1 Stahl (’97), p. 82, &c. 
