IV INTRODUCTION. 



tlie magnification employed. That there are faults no one will 

 deny ; but, on the whole, we are not prepared to condemn it as 

 unworthy of the time at which it appeared. A comparison of 

 the Desmids with those in Ralfs' work, of but three years 

 later, will show that in execution something was left to be 

 desired. 



The third epoch is one on which we must necessarily be very 

 brief; coming so near our own time we must be content to in- 

 dicate what has been done, and leave conclusions to others. 

 Closer relations with the Continent, cheap postage, more general 

 acquaintance with foreign works, all tend to raise greater expec- 

 tations for the closing work of the third epoch than of its pre- 

 decessors. The works of Kutzing, the Memoirs of Pringsheim, 

 De Bary, Colin, Bornet, Thuret, Borzi. Wittrock, and many 

 others, all contribute to illustrate British Fresh-Water Alga? ; 

 and although during forty years very little has been done in our 

 own island, even in the identification of species, there has been 

 considerable activity in investigation, especially in the North of 

 Europe. The scattered memoranda, notes and observations of 

 Professor Henfrey, Dr. Braxton Hicks, and Mr. "W. Archer 

 constitute the bulk of our home manufacture of the literature of 

 Fresh-Water Alga3 for about 30 years. The later portions of 

 the " Supplement to English Botany," containing Algre, date 

 from 1843 ; and Harvey's second Edition of the " Manual," in 

 1849, was wholly confined to Marine species. Hence there is 

 not an independent work on British Fresh-Water Algse belonging 

 to this third epoch, the only contributory work being Berkeley's 

 " Introduction to Cryptogamic Botany," in 1857. But if there 

 was an extraordinary dearth of books on this subject after 1845 

 in Britain, such was not the case on the Continent. The con- 

 secutive publication of the volumes of Kutzing's " Tabular ' 

 must have been an important influence, although it was not 

 until 1864 that Eabenhorst's " Flora Europsea Algarum, Aqua? 

 Dulcis et Submarine " was commenced. The advent of this 

 work was hailed with pleasure, notwithstanding its many faults; 

 and various authors set themselves to work on different genera 

 and families, such as ^Edogoniacea?, Zygnemacea?, &c., so that 

 in twenty years it is left far behind. As a work written in Eng- 

 lish, although not containing much original observation, we 



