1885.] HISTORICAL NOTICE OF CELEBRATED TREES. 85 



HISTORICAL NOTICE OF SOME CELEBBATED TBEES} 

 Part I. — The Baobab and the Cypkess. 



INDICES OF AGE. 



THERE is scarcely any person who knows what a tree is who 

 has not observed that the wood consists of concentric layers 

 or rings, and tliat one of these layers is deposited every year. The 

 bark also which surrounds the wood consists of the same number of 

 concentric layers as the wood itself. That such is the structure and 

 mode of growth in most cases, indeed in all cases except in the 

 Palms and their allies, and which, therefore, we leave out of con- 

 sideration, any one may readily convince himself. It affords a 

 simple mode of ascertaining the age of a tree by counting the annual 

 rings on a cross section of the trunk. It is true that in trees of 

 slow growth and great age the zones are so crowded and so numerous 

 that it is impossible to count them with accuracy, but when fairly 

 deciphered we may rely on its correctness. But the venerable 

 trunks, whose age we are most interested in determining, are rarely 

 sound to the centre ; and if they were, even the paramount interests 

 of science would seldom furnish a sufficient excuse for cutting them 

 down ; so that this decisive test can seldom be practically employed, 

 except in the case of comparatively young trees. 



When such a section cannot be obtained, we are obliged to resort 

 to other and less direct evidence, affording only approximate con- 

 clusions. Sometimes lateral incisions, not endangering the life of 

 the tree, furnish the means of inspecting and measuring a consider- 

 able number of the outer layers, and of computing the age of the 

 trunk from its diameter and actual rate of growth. But as young 

 trees grow much more rapidly than old ones, we should greatly 

 exaggerate the age of a large trunk, if we deduced its rate of growth 

 from the outer layers alone. It is therefore requisite to ascertain 

 by repeated observations the average thickness of the layers of 

 young trees of the same species, and by the judicious combination 

 of both these data, a highly probable estimate may often be 

 obtained. When unable to inspect any portion of the annual layers 

 of remarkable old trees, we may occasionally have other indications 

 upon which some reliance may be placed : such as the amount of 

 increase in circumference between stated intervals ; but, on the one 

 hand, we can never depend on the entire accuracy of two measure- 

 ments made at widely distant periods, and, on the other, the growth 

 of a small number of years, however carefully ascertained, would be 



* From a MS. of the late Professor Walker Arnott, M.D., who for many 

 years occupied the Chair of Botany in Glasgow University. 



G 



