THE DOUGLAS FIR IN SCOTLAND. 



233 



This table exhibits some very remarkable facts. In the first 

 place, it shows that the tree was still making good increment at an 

 age of 515 years, which is higher than that usually attained by the 

 European larch, Scots pine, spruce, and silver fir. Secondly, it 

 shows that the enormously rapid increase of the diameter during 

 the first twenty-five years is suddenly followed by a much smaller 

 and an approximately even increment during each of the following 

 nineteen periods of twenty-five years. I have represented the 

 progress of the diameter increment in the following drawing, which 

 will eive a clear idea of it : — 



100 



so 



80 

 70 

 60 

 50 

 40 

 30 

 20 

 10 



50 100 160 200 260 300 350 400 450 600 



AGE IN YEARS; 



Diagram showing the increase in diameter of the trunk of the 

 Douglas Fir, according to Age. 



Thirdly, the sectional area increases, on the whole, steadily. The 

 periodic increment increases up to the age of 400 years, when it 

 commences to fall. Taken by centuries, we find that the fourth 

 century yielded the largest increment. The appended graphic 

 representation will make this clear : — ■ 



. ^L a -^^ 



I L^"^* 



100 200 300 400 500 



AGE IN YEARS. 



Diagram showing the periodic increment of every Twenty-five years 

 in Square Feet. 



