44 Arber . — On the Effect of Salts on the Assimilation 
was kept carefully shaded in summer. The medium, or 
solution of salts, was contained in glass dishes holding about 
700 c.c., and about i\ inches deep and 5 inches in diameter. 
The members of a series of experiments with different degrees 
of concentration of a salt and comparative experiments, 
were exposed at the same time and for the same length 
of time, so that the temperature and illumination were 
constant. 
Before the Algae were placed in these solutions they were 
thoroughly rinsed several times with tap water and finally 
soaked once or twice for a few minutes in distilled water to 
get rid, as far as possible, of all traces of the salts of sea water. 
A preliminary series of experiments was made in order to 
make sure that this washing, especially the use of distilled 
water, did not exercise a prejudicial effect on the Algae. As 
will be seen from Experiment II, this was not found to be the 
case. 
Experiment II. Starch-free Ulva washed in 
( 1 ) Tap water, and then 
( 2 ) Distilled water. 
Tap water only. 
Control in sea 
water direct. 
Days. 
A mount of Starch . 
moderate 
moderate 
moderate 
3 
moderate-large 
moderate 
moderate-large 
5 
large 
large 
moderate 
This result was confirmed by other experiments. 
Special mention must be made of the way in which the 
amount of starch formed under different conditions was com- 
pared. It was found easy to judge this by the eye, by 
paying attention to the distribution and the intensity of the 
colour obtained by the iodine reaction. I used an arbitrary 
scale of five degrees as follows : — 
