46 



large number of blunt teeth bent over towards the centre of 

 the mouth of the capsule. In consequence of their disposition 

 round the mouth, the collective name of peristome has been 

 bestowed upon them. 



This peristome is not present in all mosses ; in certain 

 genera it is always absent. But the majority of mosses 

 possess it, and the character of the teeth is important in dis- 

 tinguishing various species. If the peristome is breathed 

 upon, and viewed with a lens, the whole of the teeth will be 

 seen to gently raise themselves until they stand in an erect 

 position round the mouth of the capsule, and form a coronet. 



A vertical section through the capsule will reveal a 

 central pillar (columella)) supporting a disc which accurately 

 fits the mouth of the capsule and protects the tiny spores 

 contained in the capsule beneath it. Those spores are indi- 

 vidually almost invisible, but each one is capable of giving 

 rise at length to a moss-plant, similar to that which pro- 

 duced it. 



We have seen that warmth causes the peristome to erect 

 itself ; and this seems to give us the clue to its use. It is 

 composed of two separate layers of cells, each layer having 

 hygroscopic properties differing from those of the other, so 

 that when subjected to the influences of cold damp air the 

 teeth close in and protect the spores ; but when the air is dry 

 and warm they open out, and at the same time the columella 

 lengthens and the disc is pushed up to a level with the tips of 

 the teeth, so that the light spores are enabled to pass out 

 between the teeth and get scattered by the wind. If the teeth 

 opened in damp w. ather the spores would either drop out and 

 fall upon the spot already occupied by the mosses, or they 

 would cake together in the urn and refuse to come out. But 

 opening when the atmosphere is dry, they fall out so finely 

 divided that the slightest movement in the air will carry them 

 to great distances, and keep them long suspended. But should 

 the breeze carry them over moist surfaces, many of them will 

 become attached and soon will germinate. 



When the spore has absorbed sufficient moisture, the 

 outer of its two envelopes bursts, thus allowing the inner one 



