Lemaneaceae of the United States . 179 
the prosecution of the work will be found in the systematic 
part under the different species. 
I wish here to acknowledge my indebtedness to those who 
have so generously aided me in my investigations. To 
Dr. W. G. Farlow, of Harvard University, for the use of 
literature on the subject in the library, of a number of exsic- 
catae containing foreign species, for the use of the specimens 
of American Lemaneaceae in his herbarium, and for many 
words of valuable counsel during the completion of the work 
at his laboratory; to Dr. S. H. Vines, of Oxford, Eng., for 
valuable suggestions and criticisms ; to my former teacher, 
Professor Wm. R. Dudley, of Cornell University, through 
whose advice and encouragement the work was first under- 
taken ; and to Professor D. C. Eaton of Yale University, 
Professor J. A. Holmes of the University of N. C., Rev. 
Francis Wolle of Bethlehem, Pa., Dr. C. L. Anderson, Santa 
Cruz, Cal., Dr. Chas. Mohr, Mobile, Ala., Professor Edward 
S. Burgess, Washington, D. C., Mr. W. A. Setchell, of 
Harvard University, Mr. Isaac Holden, Bridgeport, Conn., 
Mr. Frank Collins, Malden, Mass.., Miss Carter, of the Boston 
Society of Natural History, and Mr. J. M. Stedman, of 
Cornell University, either for the collection of material or for 
the use of herbarium-specimens. 
I. Habitat. 
The Lemaneaceae inhabit fresh-water streams, generally 
requiring the thorough aeration which is furnished in the 
turbulent waters at rapids, falls, mill-dams, etc. They are 
also dependent to a certain extent upon the depth of the 
water and force of the stream, being seldom, if ever, found in 
streams which do not have, at the rapids, a depth of water of 
one foot or more for the greater part of the year. In some 
small streams, where at most of the rapids the water is too 
shallow for their growth, occasionally the rocks are so situated 
as to confine the water to a narrow passage, permitting it to 
dash down with considerable force upon the rocks below. 
N 2 
