140 C. E. Moss , IV. M. Rankin and A. G. Tansley. 
and woods of O. sessilijlora on upland and shallow, siliceous soils, 
so ash-oak woods tend to occur on damp, lowland, marly soils and 
pure ash woods on hilly, shallow, calcareous soils. In Somerset, 
many of the woods, e.g., Cheddar Wood, on the lower slopes of the 
Mendips belong to the ash-oak association ; while on the upper 
slopes of those hills, as in Ebbor Gorge, they belong to the ash 
association. In north Derbyshire, ashwoods free from oaks are 
numerous and typical on the slopes of the Carboniferous Limestone 
hills at altitudes up to 1,000 feet. In these woods, the ash is 
dominant throughout; whereas, in the woods belonging to the oak 
and birch series, it is abundant only in the damper situations. 
It is evident that, in any given locality, the abundance of the 
ash is connected with one of two factors, either a high water-content 
or a high lime-content of the soil. The explanation of this fact 
is not clear; the relation of the ash to soil-factors requires 
experimental investigation. 
The most frequent arboreal associates of the ash are the wych 
elm ( Ulmus montana) and the hawthorn ( Cratcegus monogyna). 
The former is more abundant at the lower altitudes and in the 
damper situations, the latter in the drier situations at the higher 
altitudes. When the ash is removed or dies out in a degenerating 
wood, the elm or the hawthorn becomes locally dominant. Societies 
of aspen ( Populus tremula) are local, and of alder rare, in the ash 
woods. Societies of yew ( Taxus baccata), beech ( Fagus sylvatica), 
lime (Tilia cordata ) and whitebeam ( Pyrus Aria) occur in ash¬ 
woods in the south-west of England ; but in Derbyshire, all these 
trees (except the beech, which is planted) are rare, while in some of 
the ashwoods to the south of the Lake District, the yew and the 
whitebeam are almost as frequent as they are on the Chalk. From 
many ashwoods oaks are entirely absent. 
Several shrubs which are characteristic of the ash-oalnvoods 
become of rare or local occurrence in the upper ashwoods, and 
some are altogether absent. The following shrubs belong to this 
category:— Clematis Vitalba, Euonymus europcens, Viburnum 
Lantana, Ligustrum vulgare, and Daphne Laureola. 
The ground societies of the ash association may be classified on 
the basis of the water content of the soil. By stream sides and in 
damp places of the northern ashwoods, a very rich and varied ground 
flora is to be found. Among the conspicuous plants of such 
situations, wood-garlic (. Allium ursinum), red campion ( Lychnis 
