136 ULOTHRICACEAE AND CHAETOPHORA CEAE 
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 
Microspora 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 Kützing. 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 
