150 Sub-formation of the Older Limestones 



altitudes, the birch locally becomes subdominant or 

 dominant (Moss, Rankin and Tansley, 1910, p. 142). 



One of the most noticeable features of the English 

 ashwoods of calcareous soils is the large number of as- 

 sociated species of trees and shrubs. For example, the 

 following plants are characteristic of ashwoods but are 

 absent or nearly absent from oak and birchwoods on the 

 older siliceous soils. 



Tilia oordata 

 T. platyphyllos 

 Ehamnus oatharticus 

 Euonymus europsBus 

 Rosa spinosissima 

 E. miorantha 

 Pyrus Aria 



Ericaceous undershrubs are totally absent from the 

 ashwoods. 



Two species which characterise sub-associations of 

 the oakwoods, namely Deschampsia fiexuosa 

 and Holcus mollis, do not occur in the 

 ashwoods. The following divisions (sub- 

 associations) of the ground vegetation will 

 illustrate the range in habitat and in floristic 

 composition which occurs within the ashwoods. 



(1) In marshy places, which occur in ashwoods by 

 stream sides, at the bottoms of the streamless dales, and 

 on slopes where springs arise, such moisture-loving plants 

 as the following occur : 



Sub-associa 

 tious of tlie 

 g^round 

 vegetation. 



