CLIMATE AND TREE GROWTH 115 



found the vegetative and reproductive optima, represent- 

 ing temperatures most favourable for growth of wood in 

 the one case, and for reproductive organs and seed produc- 

 tion in the other. Apart from exceptional cases, it may 

 be stated that any plant can be grown if the climate does 

 not exceed those limits, and it matters little, so far as 

 the existence of the individual plant is concerned, how 

 far from the optimum this limit may be. For normal 

 development of stem and fruit, however, any considerable 

 deviation from optimum temperatures is injurious. If too 

 cold, badly ripened wood and immature seed are the 

 results. If too warm, damage from drought and a 

 tendency to produce excessive but abortive seed at the 

 expense of stem growth are common features, Spanish 

 chestnuts, for instance, can be groAvn to a fair size in the 

 north of England or Ireland, but seldom ripen their fruit. 

 Larch grows in all parts of Britain, but in the south of 

 England it rarely attains a large size on dry soils, while it 

 produces seed at a very early age. Numerous other in- 

 stances might be quoted which are more or less familiar 

 to most foresters. In addition to the specific climatic 

 range, however, the individual range must be recognised 

 which enables certain individuals of any species to exist 

 or succeed above or below the average limits of the 

 species. Those who observe the effect of severe winterS; 

 of late or early frost, summer drought, etc., see that 

 certain plants in a crop of any species are more resistant 

 than others to extremes of one kind or the other. This 

 may be due in some cases to a retardation or acceleration 

 of certain stages of growth, such as late leafing, early 

 ripening, or to increase or decrease of vigour ; or in others 

 to the inherent capacity of the plant to resist exception- 

 ally high or low temperatures in or out of the growing 

 season. All or any of these characters may enable one 

 plant to escape from injury which the siJecies generally 

 may suffer from. 



