70 MISSOURI BOTANICAL GARDEN. 
I have been able to give the genus during something over 
two years. The material employed has been chiefly that 
contained in the Gray herbarium of Harvard University, 
the herbaria of Columbia College, the United States De- 
partment of Agriculture, the Geological and Natural His- 
tory Survey of Canada, and the Missouri Botanical Garden, 
and the excellent private collections of Mr. W. M. Canby 
and Mr. H. N. Patterson. My thanks are due the gentle- 
men owning or in charge of these collections, for their 
courtesy in allowing me to retain the material for the long 
time needed, and I am also indebted to numerous corre- 
spondents for the communication of smaller collections or 
single specimens. 
In all of the local floras and the herbaria of the country, 
much confusion prevails as to the species of Epilobium. 
For this reason I have referred for synonyms to Watson’s 
Bibliographical Index to North American Botany only in 
cases where little or no exception could be taken to it. 
As a rule, fewer species are distinguished than can be 
recognized by one familiar with the rather slight specific 
differences that exist, and their relative importance in dif- 
ferent groups of species. On the other hand, these differ- 
ences are often so trivial and in some cases go transient, 
and the occurrence of intermediate hybrids is so common,* 
that the opinion is prevalent that Professor Haussknecht 
has described more species than are actually determinable. 
In the study upon which the following revision is based, 
I have tried as far as possible to account for all species in- 
dicated by him and other writers as coming within our 
limits, recognizing them as valid whenever satisfactory 
reason could be obtained for doing so. It is with reluc- 
tance that I publish severalas new. It must be said, how- 
ever, that increasing familiarity with the genus strengthens 
* The very large number of communications on this subject, mainly referring to 
European hybrids, can hardly be touched on here. See Haussknecht’s Monograph, 
and references in Just’s Jahresbericht for nearly every year. Inthe descriptions of 
species, I have mentioned only those hybrids which from aberrant characters 
might be looked for elsewhere than with the species they are attributed to. 
