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specific distinctions. In the Musci the sexual organs are not rarely absent, 
and when present are not so distinctive. We must therefore rely on other 
parts for the differentiation of species. The leaves, and especially the leaf 
cells, are supposed to furnish valuable characters. We have seen, however, 
in the series we have examined that these were more or less variable, and 
that this variability depended on individual differences. The characters 
derived from the size and shape of the leaves and the size and shape of the 
leaf cells, are to be regarded as complementary to those more constant, and 
are not of themselves to be considered specific. In the species of some gen- 
era in which this variability is not so marked, the leaves and tne leaf cells 
possess a higher degree of taxonomic value. 
In his excellent work, Die Laubmoose , Limpricht places considerable 
stress upon certain anatomical characters derived from transverse sections 
of the stems and midribs. Whether these will prove more reliable than those 
more commonly employed or be more acceptable to bryologists in general is 
as yet an open question. Judging from my own observations I have no 
hesitation in saying that while undoubtedly valuable they vary more than 
would naturally be supposed, this becoming apparent when the extremes of 
growth are compared, and are therefore to be taken with due allowance. It 
cannot however be too strongly urged that in the delimitation of species the 
whole plant, and not a single part of it to the exclusion of the other parts, 
should be the subject of investigation. 
From these considerations the fallacy of requiring each individual to con- 
form in all its parts to the original type of a given species becomes evident. 
This type is just as likely to be one of the lower or one of the higher forms 
of the species in question, as it is to be an intermediate form. In either case 
exact duplicates should not be demanded. Mosses do not grow so much 
after a mathematical formula as some bryologists would have us believe. 
It also appears that a single individual is not a species, although for 
descriptive and collective purposes it may be assumed so .to be. When it 
becomes advisable, which is rarely the case, to make a new species of a sin- 
gle specimen, or when the material upon which it is based is poor and with- 
out fruit, there should be something to indicate these facts, as for instance a 
double dagger as a prefix to the name of the species. This would show that 
it was simply provisional and possibly not entitled to the rank given it. 
Just here it may be observed that new species are not so much needed, 
although they may be occasionally called for, as a better understanding of 
the limitations of those already in use. It may be further observed that to 
describe a species by comparing it with another by saying that the leaves in 
the one are a little longer or a little shorter, a little wider or a little narrower, 
the leaf cells a little larger or a little smaller, the pedicels a little longer or a 
little shorter, and this too without givingany measurements, is simply inex- 
cusable. Species so described should not be recognized, neither should the 
makers of them. 
The only way to acquire a true conception of a specific type is to study 
a number of specimens, the more the better, from as many different localities 
