ALPINE VEGETATION ON BEN-Y-GLOE, PERTHSHIRE 233 



in a horizontal direction is often determined by the height of 

 some neighbouring tuft or stone, in the shelter of which they lie. 



The attitude of many of the species may be described as one 

 of " crouching " to obtain shelter from the wind. When shelter 

 and moisture are both denied them, they have still a defence in 

 reserve. Before a prolonged drought they simply adopt a con- 

 dition of suspended animation. How long they can so live would 

 be difficult to ascertain, but they must certainly be able to lie 

 dormant for several weeks without injury. 



From the lower to the higher of the two plateaux or terraces 

 described above, the ground rises in a moderate slope, and affords 

 an excellent example of the closed Bhacomitrium Heath Suh- 

 association. The requisite conditions appear to be rapid drainage, 

 shallow soil, and a low mean temperature. Another condition 

 which has been suggested as favourable for the production of 

 Bhacomitrium heath is the absence of direct sunshine from 

 northern slopes for several months during the winter, ov;ing to 

 the low angle of elevation of the sun. The ground is also usually 

 too steep and wind-swept for great accumulations of snow. On 

 Ben-y-Gloe the drifts or Schneefiechten which we encountered lay 

 below the Bhacomitrium heath. 



Except where the thick dense carpet of Bhacomitrium has 

 been accidentally torn away, or where jutting rocks protrude 

 through its compact layers, this association in its most perfect 

 development contains few or none of the higher plants. The 

 stems of the moss become procumbent, overlapping each other to 

 a considerable depth, and the subsidiary vegetation consists 

 mainly of lichens attached to its decaying branches. Macvicar (4) 

 in alluding to the Bhacomitriiim heath says " the hepatics are 

 almost absent from it," and so we found it here. We are able 

 also to agree fully with the following statement by Moss (1) : 

 " While the closed Bhacomitrium association would appear to 

 increase the shelter for other species, it is noteworthy that the 

 proportion of Highland species is generally less in it than on the 

 more open stony waste." It is probable these remarks were 

 intended to apply to flowering plants, but they are also applicable 

 to the mosses, hepatics, and lichens. 



Tlie Bhacomitrium heath forms a delightfully soft and springy 

 carpet to the feet of the traveller, and the change from the 

 arduous toil of the heathery lower slopes is always welcomed by 

 the climber. We found the flora here, as on similar tracts of 

 other mountains, poor and scanty. It is doubtful if a prolonged 

 search even at a more favourable time of the year would have 

 added very materially to the list of species noted in the centre of 

 the moss-carpet, i. c. where the association is closed and perfect. 

 Probably, however, a considerable number of small cryptogams 

 and encroaching spermophytes might be detected at various points 

 where it merges into other formations. The paucity of species in 

 the closed Bhacomitrium heath overlying quartzite rocks will be 

 seen from the following list, in which the species are arranged in 

 order of frequency. 



