150 
OF THE MOSSES AND 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 few 
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 Muscat 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 
laying 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 
