54 EXPLOITATION OF PLANTS 
lateral branches. This natural tendency renders the 
durmast oak particularly suited for planting as high 
forest with coppice. Moreover, as it is not necessary 
to plant it so close as the common oak in order to pro- 
duce good quality wood, the amenities of the game 
covert can be preserved without diminishing the value 
of the timber. 
It is significant in this connection that the timber 
from a certain wood in Hertfordshire in which the oak 
is almost exclusively Q. sessiliflora, realises nearly twice 
the price of that from the surrounding woods where 
Q. robur is the predominant tree. 
Owing to the long period that must elapse between 
the seedling stage and the mature tree, the experi- 
mental method so largely adopted in agriculture is only 
to a very limited extent applicable to forestry. As a 
consequence the ecological method of investigating the 
natural conditions as they occur in the field, and cor- 
relating them with the quality of timber produced, 
offers the best avenue for an increase in our exact 
knowledge of the factors governing timber formation. 
Data of inestimable value to the forester are being 
slowly accumulated by the ecologist. As, for example, 
accurate determinations of the acidity, water content, 
and mineral salts present in the soils of different types 
of woodlands. 
But apart from information of this character, there is 
another line of research which the ecologist has opened 
up, and which in co-operation with the practical forester 
should yield fruitful results. I refer to the association 
of species. There is little doubt that in the past we 
have been too much influenced by the German tradition 
