I] INTRODUCTORY 7 



be recorded by the occurrence of two concentric rings 

 in one season. An extreme instance of departure 

 from the normal has recently been described (6) in 

 which a tree of Tkeobroma cacao (the cocoa tree), 

 planted in Ceylon in the summer of 1893 and felled 

 in January 1901, after a life of just over 7 years, was 

 found to have 22 rings in its stem. In this case the 

 tree shed its leaves three times a year, and each break 

 in the uniformity of its vital activities was registered 

 by the apposition of Avhat under ordinary conditions 

 are spoken of as spring and late-summer wood. 

 At Aden trees stated by natives to be very old 

 showed only five or six rings of wood, a fact connected 

 with the almost complete lack of rain and with the 

 uniform conditions of existence. 



The degree of accuracy to be allowed to estimates 

 of age founded on the number of 'annual' rings is, 

 however, of secondary importance in comparison 

 with the enormously greater hold on life possessed 

 by trees as contrasted with the higher animals. Early 

 in the nineteenth century the Swiss botanist A. P. 

 de Candolle expressed the opinion that trees do not 

 die from senile decay, but only as the result of injury 

 or disease. Trees are constructed on a plan funda- 

 mentally diflferent from that underlying the structure 

 of the highly complex human organism, and are thus 

 endowed with a sort of potential immortality. It has 

 been suggested that some of the large corals in the 



