5(o^i (' 12 ; J LIBRA.' 



LiS'HS^ V E; YALE DAWSON 



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. t 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 so treated. The first tendency is best exemplified in the 

 classical work of Kiitzing ; 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. 



