218 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
primitive woodland. As in the other woods of the district, 
game are reared and shot, and the woods are intersected by long 
straight drives. Conifers are often planted, sometimes as a pro- 
tection along the border of the woods, sometimes as ornaments 
along the drives, and are often useful as landmarks. The 
ground flora resembles that of the more shady portions of the 
ash wood. ‘The soil of the oak-hazel woods is very damp, and, 
as in the ash wood, is deficient in humus. 
My observations show that the presence or absence of 
lime in the soil is not the determining factor in the distribution 
of the dominant tree; for whilst ash is dominant in the lime- 
stone woods, yet oak is dominant in the deep marls and clays, 
which are often highly calcareous ; and, on the other hand, oak 
is dominant not only on highly calcareous marls, but also on 
the silicious soils of the district. The deep soil of the marls 
and clays and of the Greensand is favourable to the variety of 
oak with stalked acorns (Quercus pedunculata), whilst the usual 
form of oak met with on the shallow and rocky sandstone soils 
is the sessile-fruited oak (Q. sesszliflora). 
Lichens are abundant on many of the trees of Somerset. In 
some cases, particularly on old birches, fruiting specimens of 
Usnea barbata, the tree-beard lichen, are excessively common, 
and other species are equally in evidence. Though lichens are 
not parasitic on the trees, yet their occurrence in excess hinders 
normal growth and development. 
The introduction of conifers into the woods of Somerset is on 
a large scale. Pine and larch plantations are abundant, but 
there are no large spruce plantations. The larch can scarcely 
be regarded as a successful introduction, as, in every larch 
plantation examined, the larch canker (Peziza Willkommit) was 
found, and in some plantations the disease was very prevalent. 
Mixed plantations of larch, spruce, Scots pine and beech are 
common throughout the district, especially on the Mendip 
summits, at an altitude of about tooo feet. 
In small areas, it would appear that plant associations are 
determined more by edaphic or soil factors than by climatic 
conditions ; but the soil factors cannot usually be inferred from 
a geological map merely. Of the edaphic factors, the occurrence 
of humus and humous acids is one which is highly important, 
and deserving of more attention than has yet been bestowed 
upon it. W. G. Situ, Ph.D., B.Sc., 
The University, Leeds. 
