136 Ulothricaceae and Chaetophoraceae 



cannot, to say the least, be considered authoritative. Of course, 

 in the fourteen years since the publication of The Fresh Water 

 Algae of the United States, considerable progress has been made 

 in Europe, notably in the separation of the genera and species of 

 Microspore/, and Conferva, and of Ulothrix and Stichococcus. In 

 other genera, e. g., Stigeoclonium, practically no advance has been 

 made. In this country, very little critical work has been done, 

 though the issue of a considerable number of specimens in exsiccatae, 

 chiefly in the series of American Algae of Miss Tilden, and the 

 Phycotheca Boreali-Americana of Collins, Holden and Setchell, has 

 paved the way for such work and in some cases made it necessary. 

 The well-prepared specimens of confervoid algae in the latter 

 series have, for the most part, the weight of Professor N. Wille's 

 determination. Any treatment of these groups, to be worthy of 

 confidence, must be supported by a knowledge of recent literature 

 not only, but by a good degree of familiarity with the exsiccatae 

 and the older literature, particularly the works of Kutzing. This 

 element appears to have been lacking in the recent work of some 

 western investigators. 



One great source of confusion has been the incorrect deter- 

 mination of specimens, particularly manifested in the practice of 

 forcing a given form into a certain species, or in other words, 

 stretching a specific diagnosis so as to include specimens varying 

 in what is believed to be unimportant details, in order to avoid 

 burdening literature with new species. Such a policy is always 

 pernicious in its tendency, for in a great number of cases the 

 species in question is misinterpreted, and its characters changed 

 so that uncertainty results, both as to the definition of the 

 original species, and also as to the character of the form identified 

 with it. In cases of doubt it is much less confusing to make new 

 species, and when a reasonably clear diagnosis of a new form can- 

 not be furnished, it should be suppressed. 



Method of Study 



In general the method pursued in preparation for this paper 



has been inductive ; the policy has been, first, to make as many 



collections as possible, and by careful observation and comparison, 



to decide upon the distinctness of the different forms, and then to 



