of Carbon Dioxide in Ulva latissima , L. 55 
wholly or partly consumed during the next period of adapta- 
tion to a slightly stronger solution. 
On the whole I found that Ulva was very sensitive to the 
amount of sodium chloride present in the solution. In a 
solution containing only 0-005 P er cent. Na Cl in distilled 
water, I obtained a ‘ moderate ’ amount of starch in six days 
in February, and a similar amount in o-oi per cent, in a 
parallel culture. This was a larger amount of starch than 
I ever obtained in distilled water. Another culture in o-i per 
cent, under the same conditions and in the same time gave 
a ‘ large ’ amount of starch. It was found that the amount of 
starch formed in parallel cultures of the same duration in- 
creased up to a little beyond 2-5 per cent., and on the whole 
the largest amount of starch was obtained in solutions of this 
strength. It would be perhaps stretching the capacity of the 
starch-scale too far to say when the exact maximum was 
reached, a result which would depend to some extent, no 
doubt, on the vitality of the individual. As far as my experi- 
ments go I should be inclined to estimate the maximum of 
concentration as between one and five per cent. Experiments 
with higher percentages showed that the assimilation became 
smaller, as was expected from results of the observers already 
mentioned. The cause of this diminution is not very 
clear. It is true that plasmolysis may have taken place, 
a point which, from the difficulties which Ulva presented in 
the extreme smallness of its cells, I made no attempt to 
determine here or in other cases. But plasmolysis does not 
necessarily imply inhibition of carbon-assimilation, for it has 
been found that plasmolysed cells can assimilate. The effect 
is more probably due to the large quantity of the salt within 
the cells hindering the metabolism. The highest percentage 
of NaCl used was 7-5 per cent, in tap water, and, as the 
following experiment shows, the amount of starch was sensibly 
less. 
