64 Vew- Trees of Great Britain and Ireland 



In the same manner the tree at Blairoowrie, 

 having a girth of 14 feet 5 inches, is mentioned 

 as 'probably planted in 16 10.' 



Although there is abundant evidence to show 

 that old trees grow at intervals much more rapidly 

 than young ones, they do not, as I have said, grow 

 uniformly, but have periods of comparative arrest 

 of growth. This occurs in trees which have formed 

 a good overshadowing head, beneath which the 

 young shoots cannot grow on the trunk. As soon 

 as any part of this head is broken, which it pro- 

 bably is every half-century or so, rapid growth of 

 the trunk sets in. Most trees of good age afford 

 evidence of this kind — having all the branches of 

 a much slighter age than would be indicated by the 

 trunk. If then the • two periods of growth and 

 arrest be taken together, we may fairly assume that 

 the averagfe rate of Qrrowth of old trees at least 

 equals, and generally exceeds, that of young ones. 

 Without some rule, warranted by actual observa- 

 tion, we are apt to form very erroneous ideas of 

 the age of these trees. From the data already ob- 

 tained it would appear that the average rate of 

 increase is from i foot of diameter in from sixty 

 to seventy years — both in young and old trees. 

 It may be even more rapid than this, but I think 

 it better to take the lowest estimate, and for this 

 reason prefer to adopt Sir R. Christison's estimate, 

 for purposes of calculation, of i foot in seventy-five 



