40 PRACTICAL FORESTRY 
a layer of wood is formed on the inside. In parts of 
the tropics, where growth is constant and where noth- 
ing occurs to interfere with the continuity of growth, 
this process of wood formation is a continual perform- 
ance, and a wood is produced which is remarkably uni- 
form and homogeneous in nature, although I know 
of no wood entirely free from rings or grain. Where 
anything occurs in the way of frost, drought, fire, 
insect defoliation, or any other check on growth, it 
is recorded in the wood. In northern countries, 
where this check is sudden and where growth is 
wholly checked, a distinct ring, called the annual 
ring, is formed. In deciduous trees it corresponds 
with the periodicity of the leaf fall. In temperate 
regions and in the tropics, where there is a change 
of seasons, the annual ring is clearly marked; where 
the season of growth decidedly changes more than 
once in the course of a year, seasonal and not annual 
rings are produced. In cases in the north where the 
growth has been suddenly checked and then starts 
again, as would happen in case of severe drought 
or defoliation by insects, a so-called “ false-ring ” is 
produced. In fact, any change whatever which 
interferes with the activity of the tree modifies 
the amount and nature of wood production. The 
whole life history of a tree is accurately recorded in 
the rings of its trunk. Within the ring itself there 
