Phylogeny and classification 147 



of the decaying plants. Cotton ('11) has shown that two conditions are 

 requisite for this extensive growth of Ulva: (1) the absence of rough water, 

 and (2) the presence of a substratum which affords a suitable anchorage for 

 the plants. In muddy estuaries the ' byssus ' of mussels is found to be a 

 particularly secure attachment; and where sewage pollution occurs the growth 

 of the Ulva may be very rank, the smell becoming most offensive on the 

 decomposition of the plants. In some localities this t/Zva-nuisance has 

 become an acute problem, as for instance in Belfast Lough. 



Freshwater Algse of various kinds frequently prove a nuisance in reser- 

 voirs and in ornamental lakes. It is possible to get rid of an objectionable 

 growth of such Algae (Chlorophyceae, Bacillariea? and Myxophycea?) by the 

 use of minute quantities of copper sulphate. It has been shown, more 

 especially by Moore & Kellermann ('05), that the amount of copper sul- 

 phate necessary to eradicate the Algae is exceedingly small, in most cases 

 one part in two millions 1 being quite sufficient. They have also shown that 

 the actual quantity necessary to bring about the required result is dependent 

 to a great extent upon the species to be dealt with. 



A few genera of Green Alga? (along with many Brown and some Red 

 Algse) are used as food by the Japanese. The only important species are 

 C odium mucronatum, Ulva Lactuca, Enteromorpha linza and E. intestinalis. 

 In Hawaii, also, Green Alga? belonging to the Ulvacea? serve as food, ' Limu 

 eleele' consisting of Enteromorpha intestinalis, and 'Limu pahapaha' of Ulva 

 Lactuca var. laciniata and U. fasciata (consult Setchell '05). 



A large species of Spirogyra is dried and sold in bundles as a vegetable 

 for food-purposes in the markets of Upper Burma (W. & G. S. W. '07). 



In an air-dry state these Alga? contain about 3 per cent, of fat, and from 

 5 to 13 per cent, of protein, although nothing is known of the utility of the 

 protein. The percentage of carbohydrates varies very much, and the simple 

 sugars are of rare occurrence. Most of the carbohydrates in the above-men- 

 tioned Green Alga? are polysaccharides of the nature of pentosans which are 

 with difficulty utilized by the human digestive tract (Alsberg '12). 



The foregoing summary will be found useful as a brief general account 

 of the Alga? included in the Chlorophycea?, but owing to the great diversity 

 in form and structure, and the wonderfully varied life-histories exhibited 

 by the Green Alga?, no advantage would be gained by an extension of such 

 a general review. Hence, for the sake of greater clearness, a more sectional 

 treatment is both necessary and desirable. 



PHYLOGENY AND CLASSIFICATION. During recent years so many dis- 

 coveries have been made concerning the life-histories and relationships of 



1 Approximately 8 oz. of crude copper sulphate to every 100,000 gallons of water. 



102 



