DISTRIBUTION OF SPECIES 119 
range, to examine a large series of specimens from as many dif- 
ferent localities as possible. It is only by this latter method that 
one can acquire a sufficient knowledge to distinguish between 
specific characters and those peculiarities which are simply due to 
variability. It should also be remembered in this connection that 
plants which grow under abnormal conditions tend to develop 
abnormally or imperfectly, and this is most strikingly true of the 
Lejeuneae. It may even happen that a specimen bearing peri- 
anths and capsules may utterly fail to show the foliar characters 
of the species, on account of the crowding together of the fruiting 
branches. Such abnormal specimens, although interesting from a 
morphological point of view, cannot always be determined with 
certainty, and yet it is unfortunately true that many species of 
Lejeuneae have been founded on just such forms. It is sometimes 
a question as to what should be done with species whose type- 
specimens are of this character, but probably in doubtful cases the 
best course is to discard them altogether. ` 
DISTRIBUTION OF SPECIES 
As a result of his own studies the writer is able to distinguish 
twenty-three species for the United States and Canada. Three of 
these are proposed as new, one is raised from varietal rank and 
six are recorded for the first time. The remaining species have 
all been previously noted. Four of our species occur in Europe, 
thirteen are more or less widely distributed in tropical America and 
six appear to be endemic. It should be noted, however, that 
two of these six species have near relatives in Europe and that 
the remaining four are closely allied to species of tropical America. 
It is very probable also that the ranges of several of these appar- 
ently endemic species will be extended into tropical regions by 
future explorations. Three of our species, Lejeunea cavifolia, L. 
patens and Cololejeunea Macounii are distinctly northern in their 
distribution. Archilejeunea clypeata, A. Sellowiana and Colole- 
Jeunea Biddlecomiae all have wide ranges extending from eastern 
Canada or New England to or beyond the Gulf States. Aarpale- 
Jeunea ovata has been found from Virginia to northern Georgia, 
while Microlejeunea Ruthii has been collected only in Tennessee. 
Our other species are characteristically southern, although Zeyeunea 
