I] INTRODUCTORY 5 



antiquity of many of our trees whose years are 

 ^sacred with many a mystery.' The section of a 

 trunk of one of the mammoth trees of California 

 (Sequoia gigantea) exhibited in the Natural History 

 department of the British Museum, shows on its 

 polished surface 1335 concentric rings denoting 

 successive increments of wood produced by the 

 activity of a cylinder of cells situated between the 

 hard woody tissue and the bark. It is generally 

 assumed that each year a tree produces a single 

 ring, though, as is well known, an estimate of age 

 calculated on this assumption cannot be regarded as 

 more than an approximation to the truth. If this 

 giant tree, which was felled in 1890, was then 1335 

 years old, it had already reached an age of over two 

 centuries when Charlemagne was crowned Emperor 

 at Rome. The concentric rings on a tree trunk owe 

 their existence to certain structural differences be- 

 tween the wood formed in the spring and in the late 

 summer. In Sequoia, as in other members of the 

 great class of cone-bearing trees, the wood is com- 

 posed of comparatively narrow elements which serve 

 to carry water from the roots to the branches and 

 leaves. As spring succeeds winter the inactivity 

 of the plant-machine is followed by a period of 

 energetic life ; opening buds and elongating shoots 

 create a demand for a plentiful supply of ascending- 

 sap, and in response to this the tree produces a fresh 



