Calculating Age by the Trephine 57 



Excluding those figures which are doubtful or 

 obviously incorrect, and assuming the remainder to 

 be accurate, they give a ratio of growth of i foot 

 of diameter in about fifty-six years,— a much higher 

 rate of growth than that arrived at by Sir Robert 

 Christison. 



A third mode of computing the age of yews, by 

 means of the trephine, which Mr. Bowman used, in 

 old trees is, I believe, of no utility whatever, owing 

 to the fact that the external rings are not regularly 

 concentric and formed in the ordinary manner of 

 young trees, but are due, as I have shown, to the 

 aggregation of many young shoots, thus giving rise 

 to a far o-reater number of rinses than would result 

 from annual growth alone. In the Darley tree, 

 for instance, Mr. Bowman found by this method 

 that the increase amounted to i inch of radius in 

 forty - six years, whereas the actual increase of 

 girth in the last fifty-two years, at 2 feet from 

 the ground, amounts to no less than 3 feet 2 

 inches or i foot 8 lines of diameter in the same 

 period, which is a very rapid growth. Mr. 

 Bowman was himself evidently not quite satisfied 

 with his observations. They led him to think 

 that I line a year is too little to allow, and that 

 De Candolle's average ' makes old trees too young 

 and young trees too old.' For the latter he would 

 allow 2, and in the case of trees growing in rich 

 soil 3, lines a year till they had attained 2 feet 



