P 11 V. FA C E . 



Dri;ixi; a long and continuous study of the Desmi- 

 diaceae we have realised the pressing need of a British 

 Monograph by means of which diligent and pains- 

 taking students may reasonably hope to identify the 

 various species which they may happen to meet with 

 in any part of the British Isles. We have no doubt 

 that one of the principal reasons for the lack of per- 

 sistent students of these beautiful plants has been the 

 absence of a reliable British Monograph on the group. 

 Therefore, when we were asked by the Council of the 

 Ray Society to undertake the work, we consented with 

 pleasure and with a determination to place the results 

 of the investigations of many years at the disposal of 

 such a useful Society. 



/ 



The earliest recorded descriptions and figures of 

 British Desmids are found in Dillwyn's ' British Con- 

 ferva?,' 1809; Smith's 'English Botany,' 171)0-1814; 

 Greville's ' Scottish Cryptogamic Botany,' 1828-1828 ; 

 Smith's ' English Botany,' edit. 2, 1 844; and in .Tenner's 

 f Flora of Tunbridge Wells,' 1845. Ralfs also pub- 

 lished some of the results of his work in the ' Annals 

 and Magazine of Natural History ' from 1842 to 1845, 

 and in the ' Transactions of the Botanical Society of 

 Edinburgh' from 1843 to 1846. In 1845 a 'History 



