56 MOSSES AND LIVERWORTS 



gives one from the capsule of the Wood Bristle- 

 moss (OrthotricJium affine). In this instance the 

 guard-cells are situated on the outer surface of 

 the capsule wall, and the pore is said to be super- 

 ficial; hut in other cases they are formed just 

 below the surface (Plate IV. fig. 22), and here 

 the pore is said to be immersed. These pores are 

 best seen in the members of the Bristle-moss 

 (OrthotricJium) family, where they constitute a 

 feature of some importance in determining the 

 names of the various species, and it is always 

 well, therefore, in examining one of these mosses, 

 to ascertain at once, by dissecting one of the 

 capsules, and viewing it under the microscope, 

 whether the pores are superficial or immersed. 

 Needless to say that a high-power lens will be 

 necessary for such a purpose. I am not aware 

 that any theory has ever been put forth as to 

 the use which these pores serve, or to account for 

 some being immersed while others are superficial. 

 Fruit-stalk. I have already referred incidentally 

 to the fruit- stalk, or seta, but this deserves a 

 few more words of notice before we proceed, as 

 it, too, has its own special characteristics. In 

 colour it varies from pale green or yellow to 

 brilliant crimson or warm brown; while, as we 

 have just seen, it is sometimes long, in other cases 

 comparatively short, and again, at times is so 

 reduced in length as to be scarcely noticeable. It 

 is either straight, with the capsule erect at its 



