AND BUXBAUMIA. 349
In all the genera having a double peristomiuni I believe the pellucid axis more or less manifestly exists ; but in these genera there is a great uniformity in the apparent number of teeth in the outer peristomiuni ; there being no instance of actual division in this series beyond sixteen, or of a further approximation, unless in OrthotricJium, in several of whose species the approximation or even union of the double teeth by pairs takes place, while in a few others the sixteen teeth are slightly divided at the apex, and in the whole genus the pellucid axis is remarkably distinct.
The only exceptions to the actual division into thirty-two, or the structure indicating that number, in the simple peri- stomiuni of Mosses, occur on the one hand in certain species of Weissia, perhaps in Encalypta and in OctoblepJiarum, in all of which, I believe, there is a reduction to sixteen : and on the other in Po/yfric/ium, where the number is frequently increased, varying in the different species, and chiefly by multiples of sixteen, from thirty-two to eighty. In this genus also, whatever the number may be, the teeth never have a semipellucid, but rather an opake or thickened axis, and no tendency to union or even approximation is observ- able. The constant equidistance of the teeth of Poly- trichum seems to be connected with its peculiar mode of dis- semination ; for as this takes place through the interstices of the teeth, and as complete separation of the seeds seems necessary on account of their extreme minuteness, a reduc- tion in number and consequent increase of size of these apertures would probably, in some degree, prevent dis- cssi persion, while the unequal distances of the teeth might either produce a deviation from the regular figure, or an early rupture, of the tympanum, which forms an essential part in this economy.
BUXBAUMIA.
In my former paper 1 1 have proposed to preserve the genus Bmbaumia, as established by Schmidel ; and in construct-
1 [Vol. i,p. 351.]
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