48 A rber. — On the Effect of Salts on the A ssimilation 
Another series of experiments, similar in nature to those 
above described, were made in which Ulva was suspended 
in damp air. Starch-free Ulva was carefully rinsed with 
distilled water to get rid of all traces of sea water, and then 
roughly dried by being gently pressed in filter paper. It was 
then placed on a dry earthenware plate covered with a large 
glass dish, and exposed to light in a greenhouse. After two 
days in the early part of June, rather more than a ‘trace’ of 
starch, i. e., almost a ‘little,’ was obtained in the two experi- 
ments made. 
Another experiment was made in which the plate held some 
distilled water and the Alga was placed on a brass stand 
similar to those commonly used in the laboratory for holding 
slides. The Ulva was so arranged that it did not dip into 
the water in the plate and the whole was covered with a large 
glass dish as before. The Ulva was kept moist and the dish 
was covered with dew from the evaporation of the water. In 
five experiments out of six a similar result was obtained to 
that in the experiments last mentioned. The Alga did not 
seem to be able to survive such treatment for a longer 
period than two days. The results, however, agree very 
closely with those obtained when Ulva was immersed in 
distilled water. 
The conclusion I arrived at from these experiments, was 
that the function of carbon-assimilation in Ulva was dependent 
on the presence of suitable inorganic salts in the medium. 
It seemed clear for the reasons already given that these 
results could not be attributed to any prejudicial effect of 
the distilled water as a medium, but that the inhibition of the 
carbon-assimilation was caused by the entire and continued 
absence of nutrient salts, just as much as it might have been 
by unsuitable physical conditions. As might be expected, 
a prolonged continuance of this condition was found to be 
fatal. 
In most of the experiments with distilled water it was 
found that a small amount of carbon-assimilation was possible, 
but the amount of starch-accumulation was never ‘ moderate ’ 
