The Ulothricaceae and Chaetophoraceae of the United States 
By Tracy. ELLIOT HAZEN 
INTRODUCTION 
The purpose of the subjoined work is to furnish a contribu- 
tion to the systematic knowledge of a group of our common but 
comparatively little known green algae. 
This work was begun about five years ago. After a some- 
what general study of the algae in field and laboratory, the con- 
viction grew upon us that the species included in the two families 
here considered form the most generally neglected and misunder- 
stood group of importance among the filamentous algae. 
The chief reason for this state of affairs is, perhaps, to be found 
in the fact that in these groups specific and even generic distinc- 
tions, for the most part, do not rest upon fruiting characters as in 
other large groups (e. g., in the Conjugatae and Oedogoniaceae), 
because there is too little diversity in such features, and also too 
little knowledge regarding them ; but such distinctions must de- 
pend very largely upon vegetative characters. These vegetative 
characters are always more or less variable and this fact has given 
rise to two opposed tendencies, either of which leads to confusion. 
On the one hand, certain algologists have treated as distinct species 
or varieties (though generally without adequate description) all 
variations found, paying very little attention to the genetic connec- 
tion which may exist among such forms ; on the other hand, some 
writers have shown strong inclination to make wholesale reduc- 
tions to varietal rank, without any sufficient understanding of the 
species sotreated. The first tendency is best exemplified in the 
classical work of Kützing ; the second began with Rabenhorst and 
has reached its extreme expression in the work of Hansgirg and 
De Toni. 
The only American author who has attempted to give a com- 
plete. account of the genera included in these two families is the 
late Rev. Francis Wolle. His work was a monumental task for a 
single pioneer, but, based as it was, almost exclusively on that of 
Rabenhorst and Kirchner, with little knowledge of exsiccatae, it 
Memoirs Torrey Botanical Club, Volume XI., No. 2. 
