194 OUR FORESTS AND WOODLANDS 
these dimensions, both as to height and girth. 
If the production of timber is the main object, 
and not beautification of the landscape, the trees 
should be planted in a mass, and kept close 
together to draw them up as straight poles. 
When once their main height has been attained 
they can be thinned out freely at frequent in- 
tervals, so that their strong natural demand ‘for 
light and large growing-space may be duly met. 
This checking of premature branch formation is 
more particularly necessary in the case of the 
white willow, which will otherwise soon spread 
itself out laterally. The wood of willows being 
soft and porous, the pruning of large branches 
is always attended with more than ordinary risk 
of fungous disease in the shape of rot occa- 
sioned by kinds of Polyporus; and this remark 
also applies to the poplars. 
The wood of the poplars is put to very much 
the same uses as that of willows, only it is not so 
tough, and is therefore not endowed with such 
good technical qualities as the latter. To make 
up for this, however, the poplars are even more 
rapid in growth. They yield good marketable 
timber at about forty to fifty years of age. The 
