The Scottish Flora. 11 



But the facts are not quite so simple as one would like them 

 to be. Gunnar Anderson has shown, for instance, that the hazel 

 once occupied a much larger area in Scandinavia than it does 

 to-day. It has lost one-third of the country in which it used to 

 grow. So he concludes that the present-day mean annual 

 temperature is about 2-4 deg. C. less than in those days. This 

 is explained by the theory of a warm, dry, and genial inter-glacial 

 period following on the fourth or greatest of Ice Ages. This 

 slight lapse in the behaviour of the average annual temperature 

 in no way confuses the general succession of Arctic alpine plants, 

 birch wood, Scotch pine forest, and oak wood, which is an emi- 

 nently natural order of colonisation. 



The number of plants, the co-operation between them as 

 well as the fertility of the soil produced by each of them, is 

 distinctly greater in each step of the series. Birch and conifers 

 have winter stores of oil, not starch, and in consequence are 

 better able to resist cold than the oak (Meg. 216). Oaks will 

 displace Scotch pine if the ground is sufficiently fertile (Dengler 

 46), and a pine forest will kill out a birch wood if the soil is 

 sufificiently fertile. 



But the colonisation of Scotland by plants was a very difficult 

 affair. I think we may be sure that they had an absolutely clear 

 field before them. In the days when two thousand feet of ice 

 flowed over Dumfries, it is hard to believe that any glacial relics 

 were flourishing even upon Ben Nevis. 



The climate after the fourth or Great Ice Age had waned 

 away would be for years, or possibly centuries, atrocious ; it 

 would vary unpleasantly. Days of blinding snowstorms would 

 be succeeded by weeks of cold grey fog. Then perhaps a week 

 or two of scorching sunshine and severe drought ; and this, 

 again, would be followed by pitiless rain continuing for 

 months together. Nor was the soil inviting. The choice 

 lay between smooth polished rock-faces, glacial boulder clay, 

 which, as all gardeners and farmers know, is of all soils 

 the most heart-breaking, bare stone shingle and barren sand. 

 The first vegetation consisted almost certainly of mere stains 

 of blue or green or red algae aided by bacteria, and of 

 lichen crusts such as we can still find on {sarticularly exposed 

 and intractable rock; that is to .say, brown scytonemas, black 



