Aleae. 7 1 



'!-' 



Poole and Weymouth in England. The results of these investi- 

 gations are summarized in a chapter on the ecology of Ulva which 

 shows somevvhat of the relative importance of the factors of expo- 

 sure, water-salinity, sewage pollution and the nature of the sea bot- 

 tom, etc. A discussion on the conditions which cause excessive 

 growth follows. In contrast to most marine algae Ulva not only 

 grows in sewage polluted water, but thrives to a remarkable degree, 

 absorbing large quantities of ammonia. The result of this excessive 

 nourishment is seen in an increased rate of growth and in a much 

 larger proportion of nitrogen in the tissues. For its presence in 

 quantity on any shore two factors are however essential, viz. 1) the 

 absence of rough water and 2) the presence of a firm substratum 

 that affords suitable anchorage. In estuaries the firm rocky substra- 

 tum is usually wanting; the banks being covered with a thick 

 layer of mud, which is devoid of weed. But in many cases exten- 

 sive areas of mussels colonize the mud banks, and on these Ulva 

 linds a mooring, and occurs as an almost pure association, the plants 

 being held securely by means of the mussel-byssus. The part played 

 by the mussels in providing attachment for the Ulva is highly im- 

 portant; and the most satisfactory way at present for reducing the 

 Ulva-growth is by removing the mussel-beds. Dressing the weed 

 with copper sulphate was only partially successful. 



Tables showing analyses of £/Z7;a-fronds and water samples are 

 given, from which it is seen that the nitrogen content of the weed 

 is proportionate to the pollution of the water; so marked indeed is 

 the relationship, that the most reliable index of theaverage pollution 

 of a given river or sheet of water appears to be afforded by the 

 chemical composition of the Ulva itself. Autor's abstract. 



Letts, E. A. and E. H. Richards. On Green seaweeds (and 

 especially Ulva latissima) in relation to the pollution of 

 the waters in which they occur. (Royal Comm. Sewage 

 Disp. Rep. 7. App. III. p. 72—120. 50 tables. 1911.) 



The present report deals largely with the growth of Ulva in 

 artificial cultures, in contra-distinction to the report by Cotton 

 which concerns its growth under natural conditions. The plants 

 were grown in different strengths of sewage pollution and under 

 various conditions; and the effect on rate of growth and composi- 

 tion of the frond specially noted. 



The more important results may be summarized is follows. 



The growth is more rapid in sewage and seawater than in pure 

 seawater. In 1 per cent sewage mixtures (the amount present in 

 Belfast Lough) this increase is not marked, but with ^larger 

 amounts of sewage the growth during the months of July and 

 August may be 3 or 4 times as great. The Stimulus of sewage is 

 most powerful during the period of active growth. The nitrogen 

 content of the weed varies in proportion to the amount of pollution 

 present (as it does also in the case of naturally grown fronds). In 

 Belfast Lough the nitrogen content varies from 3 — 5 per cent, 

 whereas the figure for the pure sea water plant of Swanage is 1,13 

 per cent. The sulphur content of the weed also varies considerably 

 but the connection of the Variation with the environment is not 

 apparent. The importance of the sulphur lies in its possible con- 

 nection with the sulphuretted hydrogen which is liberated on the 

 decay of the weed and which has caused a serious nuisance in places 



