348 ECOLOGY 



with stony debris and washed-down material from the 

 weathered sandstone edge. This debris rests upon a bed 

 of fine-grained impervious shales, but the steepness of the 

 slope secures good drainage. The lowest part, beyond 

 the influence of the weathered sandstone, has a deeper and 

 moister soil formed from the shales, and is covered by 

 humus several inches in thickness. 



The dominant tree is the Sessile Oak, the subdominant 

 ones Birch and Scots Pine, with occasional trees of Moun- 

 tain Ash, Holly, and Hawthorn. There is also a small 

 group of Beeches. In the upper part the trees are small, 

 produce little shade, and the undergrowth consists of Ling, 

 Bilberry, and Hair-grass. Bracken, which is also abun- 

 dant, has thick hard leaves. A little lower, on the stony 

 slope, Ling is less abundant, Hair-grass and Bracken are 

 dominant, and there is also Bedstraw, Tormentil, Cow- 

 wheat, &c. In the lowest part, where the soils are deeper 

 and moister, the heath-plants give place to a society of Soft- 

 grass, Bracken, and Bluebell, the Bracken here, however, 

 having thinner and larger leaves than that of the upper part. 

 In a wet hollow in an adjoining portion of the wood occur 

 such trees as Alder, Willow, and Bird Cherry, as well as 

 the characteristic trees of the wood, while the ground flora 

 consists of Marsh Marigold, Bitter Cress, Lady's Smock 

 or Cuckoo Flower, Greater Stitchwort, Marsh Stitch wort, 

 Marsh Violet, Hogweed, Sanicle, Yellow Deadnettle, 

 Narrow-leaved Thistle, Garlic, Rushes, Lady and Male 

 Ferns, and twenty other species. 



We thus see that in the drier, well-drained parts, the 

 species are fewer, and often possess small, up-rolled or back- 

 rolled leaves and other modifications, which enable them 

 to withstand drought. But when the water-supply is 

 constant, many more species are able to exist ; and they 

 possess no such extreme forms as do the species charac- 

 teristic of the drier and more exposed parts. We observe, 



