258 Dr. Smith's Remarks on the Generic Characters of Mosses, 
while Hoffman made a bold but unsuccessful attempt to cut the 
gordian knot, by calling almost every thing with a single peri- 
stomium Bryum, and with a double one Mnium. 
In solving this and every other botanical difficulty of the kind, 
the surest guide is that golden rule of Linnaeus, " Genus dabit 
characterem, non character genus." By this touch-stone let us pre- 
sume to try the genera of Hedwig, but with all the deference due 
to so great a master. If my corrections should prove just, truth 
may be benefited, but his immortal fame cannot be impaired. 
No one would be more eager than myself to defend it, if neces- 
sary, against any carping censors. 
The great hinges on which his method turns are the double, 
the single, and the defective peristomium, and the terminal or 
lateral situations of the male and female flowers. Of these the 
three first have the felicity, rare in botanical characters, of being 
absolute, and leading, with almost mathematical precision, to na- 
tural genera. Orthotrichum only affords some exceptions. Of 
some of the Hedwigian subdivisions of these^ different opinions 
may be formed, though there can be but one sentiment concern- 
ing the great outline. For instance, the comparative number of 
teeth, in the simple peristomium, 4, 8, 16, 32 or 64, affords most 
solid generic distinctions, and I regret that, in forming his genus 
of Didymodon, he makes number subservient to a trivial and very 
obscure circumstance, the approximation of the teeth in pairs. 
I scruple not to refer his Didymodon homomallum, in the descrip- 
tion of which he omits to notice that it has but 16 teeth, to Grim- 
mia, and the other species to Trichostomum. So all the species of 
Cynontodium, a genus distinguished from Didymodon by the flowers 
being hermaphrodite only, may be very commodiously referred 
either to Grimmia or Trichostomum, according as the teeth are 16 
or 32. And here I beg leave to observe, that this circumstance 
of 
