INTRODUCTION. 



ONE of the earliest attempts to bring together all that was 

 then known concerning British Freshwater Algae was Dillwyn's 

 ' British Confervas,' which appeared in 1809, and hardly any further 

 advance was made in Britain until the appearance in 1845 of 

 Hassal's ' History of British Freshwater Algae.' About this time 

 two very important works were commenced on the continent, one 

 being Kiitzing's ' Tabulae Phycologicae,' the first part of which 

 .appeared in 1846, and the other Rabenhorst's 'Flora Europgea 

 Algarum,' issued from 1864-68. Ralfs' ' British Desmids ' appeared 

 in 1848, and for the next thirty years Henfrey, Hicks and Archer 

 were almost the sole contributors to the literature of British Fresh- 

 water Algae, the publications of Archer being very numerous and 

 most valuable. 



From 1882-84 Cooke issued his ' British Freshwater Algae ' 

 and in 1887 Wolle's ' Freshwater Algae of the United States ' 

 appeared. Since the publication of these two books more actual 

 work has been accomplished in the investigation of freshwater 

 Algae than at any previous period, particularly by continental 

 investigators, amongst whom may be mentioned Wille, Wittrock, 

 Nordstedt, Bornet, Thuret, Lagerheim, Klebs, Hansgirg, Schmidle, 

 Chodat, Borge, Boergesen, Lemmermann, and others. In Britain, 

 Marquand, Bennett, and Roy have done systematic work in certain 

 districts, and, in conjunction with my father, I have myself spent 

 much time in the investigation of the Algae of many parts of the 

 British Islands. During this later period of approximately twenty 

 years many new phases have been discovered in the life-histories 

 of Algae, and much has been found out with regard to their habits 

 and mode of life. In addition, a great deal has been accomplished 

 in clearing up the synonymy of these plants, so that taking into 

 consideration all these circumstances, it is now doubtful if thirty 



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