MOSSES 73 



upon it, and thus to obtain a bird's-eye view of 

 the capsule mouth. Looking at this in the micro- 

 scope with a somewhat high-power lens, we see 

 what I have tried to give in my drawing, namely, 

 a small portion of the upper part of the capsule 

 wall, and in the centre of this the round mouth 

 of the capsule. Over this mouth the sixteen 

 teeth of the peristome will be observed, closing 

 down so as to almost fill up the aperture, each 

 tooth being strongly marked with a number of 

 parallel bars across its face. Some of these teeth 

 were evidently on the point of rising when my 

 mount was made, for their ends have been bent 

 back by the cover-glass used to seal the slide, 

 as indicated by the shaded portions in the figure, 

 We thus have an opportunity of getting a glimpse 

 into the inside of the capsule ; and here we 

 notice, just below the outer surface, the still 

 more delicate and transparent teeth of the inner 

 peristome, this capsule being an instance of one 

 that is provided with a double set of teeth. 

 Under certain conditions of the atmosphere, both 

 sets of teeth will stand erect round the capsule 

 mouth, and thus a free passage will be made for 

 the spores to find their way into the wide world 

 outside. I have shown this condition of the 

 peristome, on a somewhat larger scale, and con- 

 sequently more clearly, at fig. 5 of Plate V.a, 

 which represents the top of the capsule of that 

 member of the Bryum family (Bryum pendulum] 



