Development of Silviculture. 63 
In 1761 we find the first good statement of the theory 
of thinnings by Berlepsch, who advised taking out the 
suppressed trees when the sound poles were clear of lower 
and middle branches; he also accentuated the financial 
argument of earlier returns and increased value of the 
remainder. 
About the same time Zanthier recommended two thin- 
nings, namely, for conifers in the thirtieth to fortieth 
year first and again in the fiftieth year, for broadleaf 
forest first in the forty-fifth and again in the eightieth 
to ninetieth year. 
In 1765 the financial gain from thinnings is figured 
by Oettelt, and the possible reduction of the rotation due 
to thinnings is recognized by Leubert in 1774. 
Just as the thinning in polewoods arose from the need 
of utilization, so the weeding of young growths was done 
for the purpose of getting material for withes to bind the 
grain, etc. 
The removal of coppice shoots in oak plantings was 
practiced in Prussia in 1719, and the thinning of too 
dense sowings was advised by Carlowitz in 1713. Yet 
much later even such an intelligent man as Oettelt 
inveighed against the weeding out of the birch in spruce 
sowings because “nature prefers variety, with which 
preference it is not good to interfere.” 
This was in opposition to v. Langen (1745), who pre- 
scribed for the first time regular cleaning or weeding, 
especially the removal of the softwoods, aspen and birch, 
and of coppice shoots from seedling forest. 
It was also known that this weeding is best done “in 
the full sap,” in order to kill the stocks. 
