The Woodlands of England. \ 2 i 
the associated species we cannot yet say whether they are due to 
climate or not, and we therefore class them as “ floristic ” 
differences. For instance, we may cite the occurrence of such 
western species as Lithospermum purpiireo-coeruleum in the Somerset 
and not in the East Anglian woods, and of such eastern species as 
Primula elatior in the East Anglian and not in the western woods 
of this type. 
In the second place we have the difference of climate met with 
in ascending a hill-mass of considerable altitude. In the north of 
England, we find a noticeable effect on the vegetation at a height 
of about 1,000 feet (see p. 135). None of the south-eastern hills is 
high enough to produce any appreciable difference of vegetation 
from this cause. 
When we turn to the second group of environmental factors, 
those concerned with soil, we meet, on the other hand, with the 
principal factors which actually differentiate the British woodland 
types. 
Briefly, we find that the Alder-Willow series is characterised 
by a very high water-content, and that the other two principal 
series which we distinguish, the Oak and Birch series on the one 
hand and the Beech and Ash series on the other, are related to the 
lime content of the soil. When, however, either of these two series 
is subdivided, we find that the subdivisions are related to the water- 
content and to the humus-content of the soil. Further, the nature 
of the humus formed in the various soils has an important influence 
on the character of the sub-types in the Oak and Birch series ; and 
finally the available food (in the shape of mineral food-salts) may 
perhaps be decisive in determining the success or failure of certain 
tree-associations on sandy soils. 
Though the way in which the chemical factors, or the corre¬ 
lated physical factors, affect the vegetation—long a subject of 
controversy among plant-geographers—lies outside the scope of the 
present paper, there is an interaction of soil and climate to which 
we must call attention. The amount of water held by the soil in a 
given climate ( i.e ., with a given rainfall and rate of evaporation) 
depends primarily upon the texture of the soil; but with a wetter 
climate, i.e., with increased atmospheric moisture and with greater 
precipitation, especially a rainfall distributed over a greater number 
of days in the year, the average amount of water actually present in 
a soil of given texture is greater. Thus a “ light ” or relatively 
coarse-grained soil, that would bear a “ dry ” type of woodland 
