— 74 — 



a half opened fan. The structure of this cone is most easily understood by 

 consulting Plate VI, Fig. Di. The structure of this is almost exactly like 

 thiat of Buxbaumia shown on a smaller scale at 2 under B. indusiata. It 

 corresponds very closely in structure and development to the basal mem- 

 brane of the inner peristome of Bryum and Hypnum and their allies, only 

 in Buxbaumia the upper part is continuous instead of being broken up into 

 segments and cilia. 



The teeth of the outer peristome are constructed much like those of the 

 ordinary arthrodont type. They are well illustrated in figs. 4, 5 and 6 under 

 B. indusiata, and are shown in cross-section in figs. 7, 8, g, 10 and 11. In these 

 last figures the original cell walls are indicated by the lighter T shaped central 

 portion while the remainder consists of the thickening added on and forming 

 the plates or lamellae. The top of the T is the tangential wall while the stem 

 is a portion of a vertical radial wall included between the lamellae. But 

 instead of a single row of these teeth there are several as shown in fig. 2 un- 

 der B . indusiata. Outside of these teeth and between them and the outer 

 wall of the capsules is a mass of cells which is called the crown or pseudan- 

 nulus, which may perform the functions of an annulus but is in no way 

 homologous with it {B. ind. 3). M. Philibert considered these cells and the 

 several rows of teeth as homologous witti the outer rows of cells in the teeth 

 of the Nematodonteae, the several rows of teeth being composed of the 

 thickened papillose tangential walls of a portion of the peristomial tissue 

 while the pseudannulus corresponds to the outer layers of the same. 



This view is borne out by B. aphylla in which the outer teeth are almost \ 

 lacking and the pseudannulus is much thicker and is thickened and papil- 

 lose on its inner cell walls. According to this view then, the peristome of 

 Buxbaumia is formed of tissue homologous to that of the teeth of Polytri- 

 chum by the thickening of the tangential walls of a few rows of cells and the 

 absorption and disappearance of the rest of the tissue. Apparently these outer 

 teeth in Buxbaumia have no function and consequently have not become fixed 

 by natural selection. At any rate they are immensely variable in all the spe- 

 cies. In B. aphylla the outer teeth are scarcely present at all. In the closely- 

 related Weber a sessilis the inner peristome is essentially the same as in Bux- 

 baumia except that the folds are but 16 and there is but one rudimentary 

 outer row of teeth, thus approximating to the arthrodont type. How Lind- 

 berg, C. Mueller, and Braithwaite can deny the close relationship of these two 

 genera in the face of Schimper's figures reproduced here is a mystery to me. 



While this type of peristome is evidently intermediate between the 

 nematodont and the arthrodont types, M. Philibert's conclusion that it, rep- 

 resents a primitive type needs to be considered with a good deal of caution 

 in view of its evident functional and structural degeneracy. The variation 

 which Philibert notes as probably preceding the fixed types of the Arthro- 

 donteae may as well be explained by degeneracy. When we consider how 

 many other species of mosses with a similar habit, e.g. Pottia, Physcoinitriuin, 

 Plemidium, and Mollia viridula, have degenerated in respect to their 

 peristomes, it lends added weight to the theory of the degeneracy of the 

 peristomes of the Buxbaumiaceae. 



