288 Proceedings of Royal Society of Edinburgh. . [sess. 
ulva had been allowed to grow in them, it seemed to us that the 
information we desired ought to be readily obtained. 
The following experiments were therefore made : — - 
The frond of idva employed was well washed for about an hour 
in running tap water to free it from debris. It was of large size, 
its area being 147 square inches, or about 1 square foot, and its 
active surface therefore twice that amount. 
The dish in which it was placed was a circular glass vessel, with 
flat bottom and vertical sides, 8 inches in diameter and 3 inches 
high. It was provided with a cover similar to itself, and it con- 
tained in our experiments 1600 c.c. of water. In order to get the 
frond of seaweed into the dish, it was folded across the middle. 
Experiment 1 . — Assimilation of Ammonia . — A sample of sea 
water was employed which was collected from a locality in Belfast 
Lough where several small sewers discharge directly into the sea, 
and was therefore presumably polluted. The frond of ulva was 
rinsed in the dish with some of this water, which was thrown away, 
and the dish then filled with more of the same water, the air- 
bubbles entangled in the folds of the seaweed being got rid of by 
gentle pressure with a glass rod. Some of the water was analysed 
before this was done, while after a week had elapsed a quantity of 
the water was removed from the dish and also analysed. 
The results of the two analyses were as follows : — 
Original sea water, 
After contact with the ulva for 7 
days, 
Parts per 100,000. 
Free Albuminoid 
Ammonia. Ammonia. 
0-046 0*020 
0*000 0-020 
The seaweed had therefore absorbed every trace of free ammonia 
from the water, a result which was quite unexpected and highly 
interesting. On the other hand, none of the albuminoid matter 
had been absorbed, which, however, is quite in accordance with the 
known facts regarding plant nutrition. In order to verify this 
result, the ulva was allowed to remain in the same water for 
another week, when a second analysis was made with precisely the 
same results as before. 
