150 OF THE MOSSES AXD THEIR ALLIES. 



For the determination of species the capsule and its 

 enclosed spores must be quite ripe, and must still retain 

 its operculum (or lid), and calyptra (or veil). A lew 

 species (as Phascum) are destitute of an operculum ; and 

 in some (as Sphagnum) the calyptra disappears long before 

 the capsule reaches maturity. In all cases however, 

 where they are present, both lid and veil drop off as soon 

 as the spores are ready for dispersion ; an office which is 

 greatly assisted by a third organ, -which crowns the capsule, 

 and is known as the fringe or peristome. 



This last, which is sometimes single and at others double, 

 is of the utmost importance in the discrimination of genera ; 

 so much so that, in systematic works, the characters of the 

 subsections are founded on its absence or presence ; _ and 

 the Aploperistomi (plants with a single fringe), the Diplo- 

 peristomi (those with a double fringe), and the Gymno- 

 stomi (or such as are destitute of a fringe), form acknow- 

 ledged divisions in the Muscal family. 



The peristome, moreover, from its peculiar construction 

 and delicate colouring, makes a lovely object for the micro- 

 scope. A specimen is easily prepared : lay the capsule on 

 the thumb-nail of the left hand and cut it across the shorter 

 axis with a sharp knife, rather towards the summit. The 

 upper portion, which now represents a short tube, is next 

 to be cut half through vertically. The fringe may then be 

 spread out on a slide and covered with a thin glass to pre- 

 vent it from again curling up. 



The leaves may be preserved for future observation by 

 laving them between two pieces of thin glass, united at the 

 edges by asphalte. When wanted for use the specimen is 

 dipped into water, which entering between the glasses 

 moistens the leaf, and restores it temporarily to its original 

 appearance. All the more important organs may be 

 treated in the same way. By this arrangement much time 

 is saved, when it is desired to examine any particular 

 species, of which perhaps there may be but few examples 

 in the herbarium, and the specimens themselves, preserved 



