12 The Scottish JYora. 



stigonemas, grey lecidas, and the like. Now, when such a moss 

 stigonemas, grey hecideas, and the like. Now, when such a moss 

 and lichen growth has worked over bare clav or rock-face the 

 surface is by no means unaltered. Lichen and moss rhizoids 

 corrode the rock. Minute animals take refuge in the mosses. 

 Dead material accumulates under the moss, producing a 

 tiny film of mossy, lichenic and animal matter upon 

 which bacteria flourish. This condition affords an oppor- 

 tunity for flowering plants, and so the Arctic alpine 

 flora would begin to colonise the moss and lichen carpets. 

 Nothing in this flora is usually over six inches high, and 

 so it was well suited to the raging hurricanes and blizzards of the 

 time. It is an interesting fact that a very similar flora can be 

 found in Scotland to-day. Professor Smith calls it the vaccinium 

 summit flora, and describes it in Yorkshire and in Forfar and Fife 

 (Smith, Forfar and Fife). I found it also in Renfrewshire, on 

 the isolated rocky or stony summits projecting above the peat 

 mosses of the Renfrewshire hills (Robber Craigs, Misty Law, East 

 Girt Hill, Hill of Stake, Boxland, and High Corby Knowes) 

 (Scott-Elliot, "Trap Flora of Renfrewshire"). These lie 

 between 1500 and 1700 feet, where one could not expect Arctic 

 alpines. But thev are exposed to the worst severities of the Ren- 

 frewshire climate. In general habit it corresponds with the 

 Arctic alpine flora. It is especially an open vegetation. Such 

 flowering plants as occur are dotted about between moss and 

 lichen carpets or stones still stained by algae or lichen crusts. 

 The dominant plant is vaccinium (blaeberry), and there are three 

 grasses (aira flexuosa, fe.stuca ovina, and sweet vernal). In Forfar 

 Smith gi\es a list of the constituents, in which one notes besides 

 vaccinium three of the Dryas flora (loiseleuria, empetrum, and 

 salix herbacea). Fustuca ovina and carex also occur. These 

 were at altitudes of between 2750 feet and 3500 feet. 



The point which I wish to make clear is that in both Forfar 

 and Renfrewshire the colonisation of the highest and most exposed 

 summits has not got beyond the Arctic alpine stage. These 

 summits remain in this Dryas flora condition physiologically, and 

 some of the plants are identical. 



But when we try to trace the history beyond the Dryas flora, 

 when we look for a I)irch zone, a Scotch pine forest, and an oak 



