210 
THE PLANT WORLD. 
tissue to meet the increase in size. When the tree becomes old 
the leaf-bearing twigs become fewer and fewer, the topmost 
branches gradually dying. As the leaf surface decreases less 
food is made so the annual rings become narrower until growth 
stops and the tree is dead. Thus we see that there are three 
periods in the life of a tree, the first while it is increasing in all 
directions, the second while it remains almost unaltered and the 
third is its period of decay. 
This proves that the De Candolle’s theory is false and that 
the age of a tree cannot be determined by ratios. The sixteen- 
century belief is untenable, but some idea of the age of the Cow- 
thorpe Oak may be gained by comparing it with other oaks whose 
age is known and by considering* as much of its life as has been 
recorded. 
The large oaks at Castle Howard growing under the most 
favorable circumstances and known to have been planted early 
in the eighteenth century, have entered the period of decline. 
Others nearby which were in their prime when these were planted 
are now in the state of the Cowthorpe Oak. Judging by these 
trees we shall find that oaks under favorable conditions will live 
350 or 400 years. It seems absurd to ascribe 400 years as the 
duration of the life of the Cowthorpe Oak which for more than 
half a century has been regarded as nearly as old as the Chris¬ 
tian era, but this is about the term which trustworthy evidence 
warrants. 
The rapidity of the decay of the tree also points to the shorter 
term of life. Pictures of the tree as late as 1776 represent it as 
sound and it was not spoken of as being otherwise till many years 
later. This allows only a century and a quarter for the decay 
of the tree. From these facts it seems that 500 years is the 
longest period that can reasonably be assigned as the age of the 
tree. Popular convictions are hard to eradicate and, for many 
years to come, the old tree will probably be described as having 
lived sixteen centuries. S. G. S. 
