118 THE DEVELOPMENT OF BRITISH FORESTRY 



formation of new leaders after continuous injury from 

 frost, suckering, etc., may be considered as acquired by 

 the species to meet certain contingencies, and may be 

 brought about more quickly, but in any case must 

 occupy centuries of time, and be spread over numerous 

 generations. 



It is doubtful if any species introduced within the last two 

 or three hundred years shows any definite signs of having 

 acquired such characters. The individual climatic range 

 may more often exceed the specific in some species than in 

 others, as is evident from the fact that certain species from 

 warm climates may survive our winters in large numbers, 

 while others fail altogether. This is probably due to the 

 overlapping of species from colder and warmer climates 

 which is common in all floras. The birch and willow grow as 

 far north as the Arctic Circle. The Spanish chestnut and 

 walnut are indigenous to Southern Europe, but all are 

 capable of meeting on common ground in Central Europe 

 as indigenous trees. Scots pine represents another type 

 of a tree Avhich appears to be practically ubiquitous from 

 the Mediterranean to the Arctic Ocean. Differences are 

 also due to the winter and summer climatic ranges, the 

 former determining the lowest temperatures the species 

 is called upon to endure, the latter the heat it requires 

 or receives for its normal vegetative or reproductive 

 development. 



While the temperatures of the British climate never 

 fall below the winter minimum of any European species, 

 they do not reach the summer minimum, so far as normal 

 development is concerned, of several, such as the Cork 

 oak, walnut, Spanish chestnut, etc. In the south of 

 England the two last-named succeed fairly well, but in 

 the other parts of these Isles favourable soils and situa- 

 tions are necessary to bring them to any size. In a 

 general way, therefore, it may be assumed that the only 



