152 Sub-formation of the Older Limestones 



-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 edaphically 

 complementary and the shoots seasonally complementary. 

 In the oak and birohwoods, 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 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^ who mentions the plant as one of 

 fifty " xerophilous " plants typical of " dysgeogenous " or 

 calcareous soils. 



(4) The dry parts of the ashwoods are characterised by 

 stretches of ground ivy (Nepeta hederacea), which remains 

 green throughout the whole year and 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 hly-of- 

 the-valley (Gonvallaria majalis) and the stone-bramble 

 (Ruhus saxatilis) form fairly extensive plant societies, 

 and in these the nodding melic-grass {Melica nutans) 

 sometimes occurs. 



(5) The very driest parts of the ashwoods occur on 

 the rocky knolls. Here the soil is extremely shallow, and 

 in places the bare rock protrudes. Trees and shrubs are 

 absent, and the absence of shade allows of the growth of 



1 Thurmann, 1849. 



