II] WOODLAND ASSOCIATIONS 73 



the beginning of April, in the Derbyshire dales, the dog's 

 mercury is about three inches high : its leaves are beginning to 

 unfold ; and a few stamens are ripe. At this time of the year, 

 the moschatel is here flowering abundantly, and is almost 

 hidden by the young shoots of the dog's mercury. In the 

 fairly dry portions of the ash woods of the Peak District, this 

 ground society of dog's mercury and moschatel is a character- 

 istic feature. The society is an excellent example of what 

 Woodhead(1906: 345) would term a "complementary" society, 

 as the roots of the dog's mercury reach down to lower layers of 

 soil than the roots of the moschatel, whilst the small and delicate 

 shoots of the Adoxa receive their necessary shade from the larger 

 and more vigorous shoots of Mercurialis. Before the end of 

 June, Adoxa has entered on its long period of dormancy ; and 

 the dull green leaves of the dog's mercury, hiding its ripening 

 berries, occur in extensive and monotonous stretches. It may, 

 therefore, be said that the roots of the two species are edaphi- 

 cally complementary and the shoots seasonably complementary. 

 In the oak and birch woods, the dog's mercury occurs in more 

 or less local patches, and Adoxa is extremely rare ; whilst the 

 Mercurialis-Adoxa society does not occur. 



The dog's mercury is much more abundant, especially as a 

 social species, in English woods on calcareous soils than in those 

 on non-calcareous soils ; and this is a partial confirmation of an 

 observation made by Thurmann (1849) who mentions the plant 

 as one of fifty " xerophilous " plants typical of " dysgeogenous " 

 or calcareous soils. 



Still drier parts of the ash woods are characterized by 

 stretches of ground ivy (Nepeta hederacea) which remains green 

 throughout the whole year and which flowers from early spring 

 to late summer. If the ground is stony and composed of old 

 screes, taller herbs occur, such as the hairy St John's wort 

 (Hypericum hirsutum), the nettle ( Urtica dioica), and the wood 

 sage (Teucrium Scorodonia). These plants form close herbaceous 

 thickets in summer ; and their dead stalks remain upright and 

 rigid throughout the succeeding winter and spring. Locally, 

 the lily-of-the-valley (Convallaria majalis) and the stone- 

 bramble (Rubus saxatilis) form fairly extensive plant societies ; 

 and in these, the nodding melic-grass (Melica nutans) and Helle- 

 borine atro-rubens sometimes occur. 



