xviii INTRODUCTION. 



On the other hand the researches of Philibert and others into 



the structure and development of the peristome have necessitated 



a certain amount of reconstruction. Schimper's system, and those 



of most other authors, have been to a very great extent founded 



on characters derived from this organ ; and where groups have 



been united on the ground of supposed affinity between types of 



peristome subsequently shown to be remote from one another, 



and vice versa, it is clear that it would be wrong to ignore the 



later conclusions, and I have felt obliged in some degree to modify 



the classification in accordance with this conviction. The chief 



deviations from the usual order and grouping, and indeed almost 



the only ones of importance, will be found in the separation of the 



Grimmiacese from the Orthotrichaceae, with or near which they 



are usually placed, and their removal to the Aplolepideae, where, 



undoubtedly, they belong ; and the separation from the rest of the 



Bryales of the Nematodontoid group, including the three Orders 



Tetraphidaceae, Polytrichace3e, and Buxbaumiaceae. I have also 



discarded the usual division of the main group of mosses, the 



Bryales, into Acrocarpi and Pleurocarpi, believing that the 



characters involved in this division are far subordinate to those 



which separate them, according to the nature of the peristome, 



into the great groups of the Nematodonteae and the Arthrodonteae. 



It will be found, however, that this view does not entail any 



alteration of the usual arrangement, the pleurocarpous mosses 



following the Bryaceae in the same order as is found in most 



works. One point that it is as well to bear constantly in mind is 



that differing degrees of development between peristomes are of 



slight systematic importance compared with dissimilar types. 



Thus the difference between the gymnostomous capsule of Funaria 



fascicularis and the highly complex peristome of F. hygrometrica 



represents but a slight divergence in relationship, whereas the 



peristomes of a Splachnum and of a Grimmia, though perhaps 



almost indistinguishable except under a close microscopical 



examination, are fundamentally different in their structure and 



indicate a wide divergence of type. Carrying out this principle 



it is undoubtedly the soundest method of classification to group 



the cleistocarpous genera and species of mosses with those to 



which upon the ground of vegetative and other characters they 



appear most nearly allied, not to unite them together in a separate 



group ; and although this method entails a slightly greater 



difficulty in the identifying of the species in question, it undoubtedly 



presents to the student a more natural and therefore more 



scientific arrangement. 



