462 



BOTANY OF THE LIVING PLANT 



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. Sometimes 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. 356), or from a creeping rhizomatous shoot from which 

 the upright stems arise (Fig. 355). Their stature is never great, 

 and often they are very minute. Though they are commonest where 

 moisture is plentiful, and sometimes grow actually in water [Fontinalis), 



Fig. 356. 



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

 soil-level. B is a young gemma. kn = a bud that would grow into a new plant. 

 (After H. Muller.) 



or along its edge (Porotrichum alopecurum), 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-history of a Moss is by starting 

 from the spore (tetraspore) 9hed 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 Moss, Funaria hygro- 

 metrica, commonly makes its appearance there, though none of the 



