68 o Arber . — On the Effect of Nitrates on the 
that the rate of accumulation was correspondingly long. 
It was also found to be by no means so easy as in Ulva to 
judge of the amount of starch in the thallus, even roughly, 
and for these reasons the work was finally abandoned. Clado- 
phora rupestris is undoubtedly not an obligate Halophyte, 
and it is possible that in such Algae the necessity for sodium 
chloride, which I found in the case of Ulva to be so important 
for the maintenance of carbon-assimilation, is not so marked, 
and that the plant can continue to make use of other salts, 
more especially those of fresh water, for such a purpose. 
This would seem to be the real distinction between an 
obligate and nonobligate Halophyte, rather than any in- 
sufficient selective power on the part of the former. Un- 
fortunately, however, for the reasons just described, I am 
not able to add anything for or against this supposition. 
In conclusion I have to again express my thanks to 
Mr. Darwin for the interest he has taken in the work and the 
help which he has at all times placed at my disposal. I have 
also to express my indebtedness to the Director, and to 
Mr. Garstang, of the Marine Biological Laboratory at 
Plymouth, for the courtesy with which every facility was 
afforded for the work which I carried on there. 
Conclusions. 
(1) The addition of a nitrate to sea water causes an inhibi- 
tion of the carbon-assimilation. 
(2) With ammonium nitrate, the inhibition is very marked, 
and the presence of this salt is quickly fatal. 
(3) Potassium nitrate causes a more marked inhibition 
than sodium nitrate. 
(4) Magnesium nitrate, the nitrate occurring in sea water, 
causes the least marked inhibition. 
(5) Potassium phosphate added to sea water in an appre- 
ciable percentage, causes a considerable inhibition. 
(6) In the thallus of Ulva , Enteromorpha and Cladophora , 
there is a marked storage of starch, and a very slow rate of 
translocation. 
