Nov. 1802.] BOTANICAL SOCIETY OF EDINBURGH. 459 



or felled trees, from counting the annual rings. The 

 correspondence between these and the age may not be 

 precise in the stems of very old trees, as they may 

 have ceased to lay on wood below while still growing 

 above, but the method is probably reliable enough up to 

 a very considerable age, although rarely, if ever, available 

 in the case of aged veterans. 



At one time it seemed as if a simple and reliable mode 

 of estimating the age of trees had been established by De 

 Candolle, who, relying on observation of the annual rings 

 in many tree sections, published as a well-ascertained fact 

 that, after a period of greater activity in early youtlr 

 the annual rate of girth-increase continued throughout 

 life at a tolerably uniform rate. But Sir Eobert 

 Christison* showed that De Candolle must have been 

 misled by using sections taken near the ground, where 

 the tendency to a conoidal swelling as age advances 

 tends to equalize the rings ; and that above this conoidal 

 swelling, in the great majority of cases, there is a 

 gradual although irregular decrease in the width of the 

 rings with age. Hence although De Candolle's rule 

 might answer near the base, it was inadmissible higher 

 up. But Sir Eobert also showed that even at the base 

 it was unreliable, as the rings frequently vary much in 

 width there within short periods of time. Hence it is 

 not possible to ascertain the age of a tree merely by 

 ascertaining its recent rate of girth-increase. 



The age of trees even of very considerable size may 

 sometimes be estimated, in a rough way, simply by 

 measuring the girth, as pretty numerous data exist 

 showing the rate of growth and the age of trees in 

 some species at various sizes. But, in working thus 

 by comparison, it is necessary to take the circumstances 

 of each tree into consideration, and it is only in a few 

 species that sufficient data for the purpose have been 

 collected. 



It is when we come to gigantic trees, however, that the 

 most serious difficulties occur, chiefly from the almost total 

 deficiency of data bearing on their growth during the 

 latter part of their career. We may form some notion 



* Trans. Bot. Soc. Ed., 1878, p. 225. 



