350 XXV. REPRODUCTION OF THE BRYOPHYTA. 



the brim of the urn, lift it up, and place it, with the teeth turned 

 upwards, upon an object-slide. We remove the mirror from the 

 microscope, or turn the diaphragm so that ]no aperture lies under, 

 and observe the object with direct light. For this we can use 

 only a low power. We can decide that the teeth are inserted in 

 the inner brim, that they are wedge-shaped, and cross-striate. If 

 we breathe lightly on the object while still looking at it, we shall 

 see the teeth curve together inwards. They are hygroscopic ; in 

 damp weather they bend inwards, and so close the open capsule, 

 while in dry weather they bend outwards, and again open the 

 capsule. We count sixteen teeth on the urn. We now lay the 

 same section in a drop of water, and, tearing it through on one 

 side with the needles, spread it out flat, cover it with a cover- 

 glass, and observe it by transmitted light, and first from its outer 

 side. We then notice, quite at the edge of the urn, a double layer 

 of obliquely-arranged cells, papillately prolonged, pretty strongly 

 thickened, and containing abundant chlorophyll grains. These 

 cells have colourless walls, browned only at their very base, and 

 there they are very easily disconnected from the edge of the urn, 

 remaining, however, connected together. By means of these cells 

 the separation of the operculum (lid) is effected ; they form the 

 so-called annul us at the rim of the capsule. Now laying it with 

 the inner side upwards, the preparation shows us that the cross- 

 striae already noticed on the teeth are ridges projecting from their 

 inner surface. Besides the outer peristome formed by the teeth, 

 an inner one is also present; it consists of the so-called cilia, 

 Mnium hornum has, therefore, a double peristome, while there 

 are Mosses with only one, and also without any such peristome. 

 The cilia, like the teeth, are here flat lamellae, which in their 

 lower part appear divided into chambers, and in their upper part 

 cross-striate, by slight projecting ridges on their inner surface. 

 In the lower part they are fused together into a continuous mem- 

 brane, which bulges somewhat between each pair of teeth of the 

 outer peristome. Two cilia stand between each pair of teeth, and 

 present themselves obliquely from the rim. Their edges, the 

 outer in their entire height, the inner only in the upper part, are 

 fringed with small serrate projections. In these the cross-ridges 

 of the surface of the cilia end. Through these serrations the 

 pair of cilia in their upper part are combined by the [outer edge, 

 and finally the two fuse into a single narrow, elongated apex. 

 With these pairs of cilia alternate very small ones, which, from 



