IN BRYOLOGICAL WORK 531 



so elastic that some difficulty is found in keeping the peristome 

 flat when it is mounted unless pressure has been previously applied. 

 Glycerine jelly or Farrant's medium are the most convenient 

 mountants. There is really no particular reason why the peristome 

 should be mounted in its entirety, as a sector of it serves all useful 

 purposes and is very much more easily managed ; that is to say, 

 there is no additional knowledge gained by mounting the whole 

 thirty-two teeth of a double peristome when a sector embracing 

 four each of the outer and inner teeth will enable all structural 

 details to be made out. The tubular teeth of the Tortulaceae can 

 only be mounted en bloc ; the basal membrane is the point of 

 interest, and so long as this can be clearly made out the rest does 

 not matter. 



In some species the teeth of the peristome are extremely 

 fragile, and it is rarely possible to get satisfactory mounts of 

 them if one relies on finding a perfect specimen in a chance 

 gathering. I believe the only way is to bring home unripe 

 specimens and carefully ripen them under observation, so that 

 the capsule can be mounted as soon as the ripe operculum falls. 



The capsules of the Orthotrichaceae bear very important char- 

 acters in the presence of stomatic cells. These are of two forms ; 

 in the one they are seated in the cuticle only and are " superficial," 

 in the other they are buried in the wall of the capsule and are 

 " immersed." To get a good view of them the capsule is slit up 

 and the spore ^ac removed. The capsule is then spread out on 

 a slide, cuticular side uppermost, and mounted in glycerine jelly. 

 The stomata are said usually to be found in the lower half of 

 the capsule, and they are certainly always found there in the 

 books ; but occasionally nature seems to ignore her own boundaries, 

 for I have seen them scattered here and there over the capsule, 



As I have previously stated, a student's collection of slides 

 would be no incentive whatever to any one to take up the study 

 of mosses. At the same time I can imagine no more valuable 

 collection than a reference series of slides of closely allied species, 

 and species subject to wide variation. The determination of 

 species and varieties in the moss flora has become a matter of 

 extreme difficulty, thanks to the efforts of specialists in various 

 groups, and even an advanced worker is glad of anything that 

 looks like finality. Fifty years ago English bryologists con- 

 sidered themselves well served with ten species of Sphagna, the 



