RING-MARKS OF THE STEM. 103 
marked irregularly with holes, endogens or mo- 
nocotyledons. 
LEAF OF AN EXOGEN, LEAF OF AN ENDOGEN. 
We have just said each of these rings stands 
for a year. As will therefore be quickly ima- 
gined, we have only to count up how many rings 
there are from the centre to the circumference, 
and we shall learn how many years have passed 
over the head of the tree, or, in other words, how 
old it is. And this is, in fact, a very sure guide ; 
for the rings form a very correct register of the 
age of the tree. A singular use has been made 
of this fact, which deserves remembering. Many 
of our readers are probably aware that the coal 
which we burn for fuel was a very long time 
