72 THE SCOTTISH BOTANICAL REVIEW 



in the soil-waters than most other British trees. It is light- 

 demanding, and therefore unfitted for competition in close 

 canopy, but reaches perfection with greater humidity and 

 cooler summer temperatures than Q. pedunculata. In oak- 

 woods it is frequently confined to wet flushes in sloping 

 hollows, where often a very black humus is formed from 

 forest litter apparently under the influence of alkaline 

 drainage. The oaks avoid these damp spots perhaps for 

 similar reasons that they avoid most limey soils, but whether 

 this be from excess of salts in solution or for other reasons 

 remains to be shown. Many acid-humus and cold-enduring 

 plants appear to succumb to very slight excess of mineral 

 food in the soil-waters, and it is probable that the diff"erent 

 forest-trees have very different optima in respect to the 

 strength of mineral soil-solutions about their roots. 



Ash-trees probably find somewhat similar conditions to 

 those of the flushes, in the soil in the crevices of limestone and 

 amongst debris on steep limestone slopes in which they 

 deeply root. A habitat where it can root deeply, obtaining a 

 relatively large supply of mineral food-solutions and yet avoid 

 competition with the oak or beech, appears to be the natural 

 one for ashwoods. 



The influence of physiography in causing contrasting 

 habitats in limestone areas has already been referred to, and 

 the beech has very different capabilities of rooting to those 

 of the ash. A deep, well-drained, uniformly good soil may 

 perhaps induce deep-rooting in the beech ; but with its dislike 

 for undrained soils and with its great spread of strong, com- 

 paratively superficial roots, it appears often to have specially 

 selected a slightly raised, rocky mound when growing in oak- 

 woods. In the Lowlands of Scotland raised mounds, due to 

 small exposures of whinstone or other rock, are frequently the 

 site of small but strong beech-clumps. These of course are 

 plantations, but may be the successful trees out of mixed 

 plantings. Beech-trees growing on poor, loose soil are 

 frequently uprooted by storms, but those growing upon the 

 rock escape. Their success on the bare chalk may then 

 perhaps be accounted for by their power of strong superficial 

 anchorage, and the deep shade and abundant leaf-fall with 

 which they protect the surface from evaporation. 



