200 



THE BOOK OF NATURE STUDY 



many parts of Yorkshire, pine woods are to be found on the edge 

 of heather moors. At the present time many of those moors, 

 especially in Scotland, are preserved as grouse shootings, or as 



sheep-walks. In order to preserve a 

 good growth of young heather, the old 

 is often burnt. It has been found 

 possible, too, to reclaim many of the 

 Cotton-Grass moors by letting sheep 

 graze on them ; then the Heather 

 gradually re-establishes itself where 

 the Cotton-Grass formerly was ; thus 

 the burning of the Heather and the 

 improvement in drainage may in time 

 convert a Cotton-Grass into a Heather 

 moor. In ways of this kind the vege- 

 tation of a district may in course of 

 time be considerably altered by man. 



GRASS HEATHS 



Grass Heaths occur at all altitudes 

 above 1000 feet. They often form a 

 transition between cultivated land on 

 the one hand, and the Heather moor 

 on the other. The two grasses most 

 characteristic of these heaths are : (i) 

 The Moor Mat Grass (Nardus stricta), 

 one of the dominant plants of dry 

 heaths ; and (2) the Purple Molinia 

 (Molinia ccerulea), characteristic of wet 

 heaths. The former is easily recog- 

 nised in autumn and winter by the 

 white colour of the dead stems. It 

 grows on well-drained steep slopes, 

 ,very often on glacial debris, either 

 with no peat at all or with a very 



FIG. 62.-Purple Molinia (Molinia thin l ^^' The Pui *P le Molinia, as it 



is called from the purple-blue flowers, 



