Page:An introduction to physiological and systematical botany (1st edition).djvu/522

 492 has been laying down certain principles as absolute in forming genera, without observing whether all such genera were natural. Such mistakes are very excusable in persons not conversant with botany on a general scale, and whose minute and indefatigable attention to the detail of their subject, more than compensates the want of what is easily supplied by more experienced systematics. Thus Barbula of Hedwig is separated from Tortula, ''Engl. Bot. t. 1663, and Fissidens from Dicranum, t.'' 1272, 1273, on account of a difference of form or situation in the barren flowers, which is evidently of no moment, and merely divides genera that ought to be united. The same may be said of genera founded on the union of the stamens and pistils in one flower. On this subject I have been more diffuse in a paper on Mnium, in ''Tr. of Linn. Soc. v.'' 7, 254, to which I beg leave to refer those who are desirous to study it further. Various and abundant specimens of this tribe of plants, showing the various structure of the fringe, lid and other parts, may be