268 
Proceedings of Royal Society of Edinburgh. [sess. 
The Seaweed Ulva latissima, and its relation to the 
Pollution of Sea Water by Sewage. By Professor 
Letts and John Hawthorne, B.A., Queen’s College, Belfast. 
(With Three Plates.) 
(Read March 4, 1901.) 
Por a number of years a very serious nuisance has arisen from 
the ‘ sloblands ’ of the upper reaches of Belfast Lough during 
the summer and early autumn — the stench at low tide being 
often quite overpowering, and the air heavily charged with 
sulphuretted hydrogen. 
A precisely similar nuisance, though not of the same magnitude, 
arises from the sloblands in the northern portion of Dublin 
harbour. 
This nuisance, in Belfast at all events, has been supposed by 
many people to be due to sewage matters actually deposited on the 
slobland, but it requires but slight observation to prove that this 
can scarcely be the true explanation, for without doubt the 
nuisance is intimately associated with deposits of green seaweed, 
consisting almost entirely of the Ulva latissima , or, as it is 
commonly called, the ‘Sea Lettuce.’* 
* That others have noticed the occurrence of this seaweed in polluted sea 
water, and the nuisance which may arise from it, is shown by the following 
letter which we received from Professor Hartley, F.R.S., of the Royal College 
of Science, Dublin, during our investigation on the subject : — 
“Professor Johnson has shown me your letter in re the sewage of Belfast 
and the shore weed. That weed is never seen on any shore unless sewage runs 
into the water. The stronger the sewage and the greater its volume, the 
more luxuriant its growth. I have observed this during the last twenty 
years in England, Wales, Ireland, and Scotland. About eight years ago I 
washed some of the weed in fresh sea water and placed it in a bottle of the 
same. In about twenty-four hours the bottle was opened and the contents 
found to be in an exceedingly offensive state. 
“A paper of mine in the Proe. Eoy. Soc. Edinburgh , session 1895-96, 
touches upon this matter.” 
Nothing, however, appears to have been published on the subject, and we 
are under the impression that most botanists consider Ulva latissima as 
characteristic rather of brackish than of polluted sea water. 
