vi Preface 



The magnifications given under the figures are far from uni- 

 form, but this is no great disadvantage, as a knowledge of the 

 relative sizes of these plants is very soon acquired, and ' size ' is 

 of no generic and little specific value. 



Accurate measurements are given of the most abundant and 

 widely distributed species. 



It was originally my intention to add a chapter on the Pcri- 

 diniea:>, but after further consideration I have for two reasons 

 excluded them. Lack of space would have compelled me to have 

 given a veiy indifferent account of them, and I also prefer to 

 regard them as a group quite distinct from the Algae. Most 

 zoologists claim these organisms as Dinoflagellates, and the Peri- 

 dinieas of this country are sufficiently numerous and important 

 to require separate treatment. 



Similar remarks apply to the Characese. They are best re- 

 garded as distinct from the Alga3, as their vegetative organs 

 exhibit far more differentiation than the vegetative structures of 

 any of the freshwater Algse, and their sexual reproduction is of a 

 distinctly higher type. 



In some instances I have quoted freely from previous publi- 

 cations of my own, sometimes with slight alterations. 



The work was undertaken at the request of Mr A. E. Shipley, 

 to whom I tender my best thanks for assistance and advice during 

 its publication. I have also to thank Mr Edwin Wilson for the 

 care he has expended in reproducing the drawings. 



I take this opportunity to remark that a good systematic text- 

 book of British Freshwater Alga?, with descriptions of all the 

 known species, remarks on their affinities, and if possible, with 

 figures, is at the present time very urgently needed. There is, in 

 fact, no single book, or set of accessible books, by means of which a 

 student can hope to accurately identify one-third of the freshwater 

 Algae he may find in a single day's ramble through a reasonably 

 productive part of the country. I venture to state that this is 

 the only branch of systematic botany in which such a state of 

 affairs exists. 



The reason for it is not far to seek. It is one result of the 

 general neglect of systematic botany (especially Cryptogamic) in 

 the botanical laboratories of this country. Every encouragement 



