58 THE BOOK OF FORESTRY 
Regarding the rate of growth certain of the hard- 
woods, like chestnuts for instance, are more lasting if 
they have grown rapidly; evergreens generally are more 
durable if they have grown slowly as there is a greater 
proportion of the heavy summer wood in the annual 
ring. , 
Thus hardwoods are likely to produce their best and 
most durable lumber when grown in the open on good 
soil, while the reverse is claimed to be true for the ever- 
greens. 
With the rapid increase in the use of preservatives 
a tree nowadays need only be hard. Resistance to 
decay can be acquired through chemical treatment. 
(See Chapter XII.) 
Weight.—In spite of the fact that the wood substance 
produced by all tree species is the same weight—a 
little more than one and a half times that of water— 
the timber sawed from different trees varies consider- 
ably in weight. This is due to the compactness of 
arrangment of the wood fibers and the amount of air 
contained in the wood. Most of the pines will float 
when green, but after they have been in the water 
Some time they become heavier than water and sink, 
owing to the fact that water has replaced the air. Both 
on account of the compactness of their structure and 
their moisture content few of the broadleafed trees will 
float, although some will do so after being dried out. 
The amount of heat that is obtained on burning wood 
depends largely on its weight and such heavy species 
as hickory, oak, and sugar maple yield the hest fuel 
wood; in fact there is a direct ratio between the weight 
of wood and the heat it liberates upon burning. In 
a general way it may be said that the heavier woods 
are more valuable, as they are likely to be stronger 
