MUSCI AND HEPATICAE 



355 



upon localised absorption by these, but also upon general absorption 

 by their whole surface, as opportunity offers for it. 



Musci, OR Mosses. 



Mosses are usually gregarious. The leafy plants are often massed 

 together in tussocks or cushions with their small stems upright, and 

 occasionally branched. Or they may be isolated and straggling, with 

 more frequent branchings. They are fixed in the soil or some other 

 substratum by numerous rhizoids springing from their base (Fig. 297), 

 or from a creeping rhizomatous shoot from which the upright stems 

 arise (Fig. 296). Their stature is never great, and often they are very 



Fig. ^97. 

 Lower part of stem of a Moss {Barbula muralis) with protonema. a-b shows the 

 soil-level. B is a young gemnaa. kn = ^ bud that \\ou!d grow into a new plant. 

 (.\fter H. MuUer.) 



minute. Though they are commonest where moisture is plentiful, and 

 sometimes grow actually in water [Fontinalis), or along its edge [Pore- 

 trichum alopecurimi) , they often flourish in stations apparently the 

 most unpromising, such as exposed rocks or roofs, tree-trunks, and 

 wall-tops. Here they may be dried to crispness in summer. But 

 they recover at once after a shower of rain. This capacity of resisting 

 drought, and of instant recovery by surface-absorption of water, is one 

 of the causes of their biological success ; for by entering thus a state 

 of physiological inhibition, they can tide over extreme conditions. 



The best way of presenting the life-historv of a Moss is by starting 

 from the spore shed from the ripe capsule. The spores are so minute 

 that they are readily carried as dust by the breeze. A striking instance 

 of their ubiquity is seen where ashes are left after a fire in woods, 

 or even on cinder paths. A certain i\Ioss, Funaria hygrometrica, 



