THE SMALL AND LARGE FRINGE-MOSSES 109 



apples. The Hairy and Silvery Thread Mosses (Bryum capillare, 

 B. argenteum) have pear-shaped capsules like those of the Mniums, 

 but they hang vertically downwards on the stalk. The former, 

 common on walls, rocks, and often on tree trunks, is a tufted 

 plant with bristle-tipped leaves ; the latter, on dry roadsides 

 and walls, is smaller (about half an inch high), and is pale green 

 when moist, but white and silvery when dry, with blunt-tipped 

 leaves. These, like the other wall-inhabiting mosses, are able 

 to endure complete drying up for a fairly long time. The Small 

 Fringe-Mosses (Grimmia) form neat, grey, rounded cushions 

 on stone walls almost everywhere, the grey appearance being 

 due to the leaf -bristles (one at the tip of each leaf). One kind 

 has a very short fruit-stalk hardly projecting from the leaves, 

 but in the commonest kind the stalk is long. The peristome 

 teeth are dull red and notched at the top ; they spread out 

 when dry. It is interesting to compare the fruits of the two 

 common Grimmias. In the very common grey-cushioned kind 

 (G. pulvinata) the stalk is at first strongly curved, so that the 

 young capsule is buried in the leaves and protected by them 

 until it is ripe, when it becomes erect. The mouth of the capsule 

 is small, so that the spores can only be shaken out gradually 

 by the wind, an important thing (to avoid waste of spores) for 

 a plant growing on an exposed wall top. In the rather less 

 common " sessile-fruited " kind (G. apocarpa), whose tufts are 

 less dense and brownish, the capsule has a wider mouth, since 

 it is less exposed to the risk of having all the spores blown away 

 at once in a high wind. The Large Fringe-Mosses (Rhacomi- 

 trium) grow on rocks more commonly than on walls, and one 

 kind (Woolly Fringe-moss) grows on moors in large cushions a 

 foot or more across. The leaf has a white hair at the tip, which 

 is often as long as the leaf itself, or longer. The Purple Fork- 

 Moss (Ceratodori), one of the commonest wall mosses, is easily 

 known by its purple fruit-stalk. The peristome is very pretty, 

 each tooth being nearly cleft to the base into two equal parts. 

 The Screw-Mosses (Tortula) have hair points on their leaves, 

 but are distinguished from other mosses by their curious peri- 

 stome. This consists of thirty-two long threads, which are 

 spirally coiled. On drying, the teeth become partly uncoiled, 



