PREFACE. VU 



Although this work is believed to be exhaustive of all now known 

 concerning the Desmid's of the United States, yet the author regards 

 it only as the pioneer to others much larger and therefore more 

 valuable, wherein will be recorded the achievements of those who 

 will perhaps be indebted to this work for their first introduction to so 

 fascinating a study as that of the fresh-water Algce of our country. 



F. W. 

 Bethlehem, Pennsylvania, 

 February, 188-1. 



PREFACE TO SECOND EDITION, 1802. 



September, 1891, found us unable to supply the occasional demands 

 for a copy of DEsiriDS op the United States. Some of the plates 

 were reproduced by means of the camera; these, in connection with 

 other plates and some copies of letterpress remaining from the 

 original pul)lication made a very limited number of complete copies, 

 which, however, soon proved in.sufiicient. The demand for more 

 encouraged the idea of another edition of the work. 



Since the original publication in 1884 quite a number of discoveries 

 were made. wSome of these were published on eight plates, and issued 

 in connection with the Fresh-water AiAiM of the United 

 States. Still later discoveries fill two more plates. Putting these 

 together we get a volume with one-fifth more plates than the original. 



To make a new edition the fact is evident that the demand for a 

 book of the kind, naturally limited, has been pretty well supplied, 

 and hence the risk of sale greatly increased. The author's consider- 

 ation must be to curtail expenses. This he hoped to do in a satis- 

 factory way by furnishing a book with many additional plates, figures 

 all hand-colored, without an increase in price. The plan was to omit 

 the descriptive part of the book as far as it relates to species, believ- 

 ing the distinct forms of the Desmids suflflcient for identification, but 

 upon maturer consideration and advice have concluded to make a 

 complete reprint, adding all known later discoveries. This will 

 add greatly to the size of the volume and isroportionately to the 

 expense, but in every other regard will make the most satisfactory 

 work for reference. 



The discoveries of species new to the United States the past few 

 years, have not been as numerous as might have been expected in so 

 great a territory as belongs to us. A few have worked with success. 

 W. L., Poteat, of North Carolina, published a preliminary list of Des- 

 mids from his State. W. N. Hastings, Rochester, New Hampshire, 

 has been doing a good work as is evidenced by the plants acknowl- 

 edged to his name. G. Lagerheim, of Sweden, received material 

 from Massachusetts containing a number of new forms. W. Joshua ; 



