62 Arber . — ( 9 /z the Effect of Salts on the Assimilation 
The conclusion which I came to was that the absence of 
normal amounts of Mg Cl 2 or K Cl did not have any appre- 
ciable effect, and that these salts alone would not have a 
very great influence in maintaining the normal amount of 
carbon-assimilation. In Exp. IX, sufficient magnesium was 
probably present for the needs of the plant in the magnesium 
sulphate, and from Exp. X, I gathered that the plant could 
manage for some little time without access to potassium. 
Experiments were also made in which Ulva was cultivated 
in various percentages of Mg Cl 2 and K Cl, all other salts 
being, as far as possible, absent. 
(A) Mg Cl 2 . 
This series of experiments was unfortunately left until 
the summer was advanced, and for this reason I was not able 
to carry them as far as I could have wished, and the deduc- 
tions which I have drawn must be regarded as provisional. 
Solutions were tried which contained 0*31 per cent, (the amount 
in sea water), 1 per cent, and 2 per cent. Mg Cl 2 made up with 
distilled water. Two series of each of these percentages gave, 
after repeated testings, either a £ trace ’ or a‘ little,’ the same 
amount which would have been obtained in distilled water 
alone. In no case was a ‘moderate’ amount obtained; and 
after a short time the Alga did not appear to be in a very 
flourishing condition. 
(B) K Cl. 
In the case of this salt a larger number of experiments 
were made, and under more favourable conditions than with 
Mg Cl 2 . Solutions of 0-07 per cent, *5 per cent., 1 per cent., 
and 2 per cent. K Cl were used. They all gave similar results. 
Either the amount of starch was nil, or a ‘ trace ’ only was 
found. In one instance the amount was almost a ‘ little,’ 
which was the largest degree of starch I could obtain. In 
less than a week the Alga usually became obviously un- 
healthy. 
