[Vor. 1 
232 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
Two main types of nutrient solution were used,—one (solu- 
tion A) being natural sea-water, the other (solution B) being 
an artificial sea-water minus nitrogen. These stock sea-waters 
were made double strength and subsequently diluted by the 
addition of distilled water and the stock solution of the nitro- 
genous compounds to be tested. The following nitrogen com- 
pounds were used in the experiments: ammonium nitrate, 
urea, acetamid, sodium asparaginate, acetanilid, and dimethyl- 
anilin. Parallel experiments were run, adding these compounds 
to solution A and solution B. 
Preliminary tests roughly determined the maximum поп- 
toxic concentrations of these compounds when added to sea- 
water to be: 
Ammonium nitrate............ 0.011 gram molecular 
с, реа 0.010 gram molecular 
Acetamid..................... 0.250 gram molecular 
Asparagin..................., 0.080 gram molecular 
The table presents the results of the experiments. All figures 
for concentrations represent fractions of gram molecules per 
liter, except in the case of dimethylanilin. Here the solubility 
was not known and the figures represent fractions of a saturated 
solution in distilled water at 20°C. In the column headed 
"growth" is recorded the increase in length in millimeters of 
the strips of Ulva after 10 days in the solution. In each case 
the figures for growth represent the average of three or more 
cultures. Checks show the growth in solutions A and B with 
no additional nitrogen. 
It is apparent from the following table that, under the condi- 
tions of the experiment, ammonium nitrate and urea are consider- 
ably better nutrients for Ulva than the other compounds used. 
These two cause a marked increase in growth over that of the 
controls, in both the artificial and natural sea-waters. The 
nutritive value of these compounds was also indicated by the 
healthy appearance of the cultures. Тһе alge were of a deep 
green color, very turgid, and considerably curled by rapid 
growth. Judging from the growth and general appearance of 
the cultures, there is little choice between the nutrient values 
of ammonium nitrate and urea. 
