NOTES ON CONTINENTAL FORESTRY IN 1905. 169 
trees attacked, as the eggs are seldom laid within 7 feet of the 
ground, and the insect is rarely found in the branches. There 
is seldom any external sign of the infestation until the bark is 
destroyed by the lateral galleries formed by the caterpillars, when 
the tree sickens and dies rapidly, and then it must be felled 
and barked at once to prevent the exit of the beetles. At first 
old trees are preferred, but in cases of large infestation trees of 
all ages are attacked. By felling 14,603 trees found to be 
attacked (measuring 640,000 cubic feet, and valued at £14,000), 
the danger has been partially overcome ; and estimating 150,000 
to each tree, this means the destruction of over 2000 millions of 
insects. There still remained the fear that a new infestation 
might occur in 1905, but climatic checks and natural enemies 
appear to have fortunately obviated this danger. 
Of other noxious insects, the oak-tortrix (Z. virtdana) has for 
the last three years, and in some localities for four and five years 
in succession, attacked pure oak-woods and mixed oak and beech 
in the Paris region, extending from the Vosges to Brittany and 
throughout the central plateau, or about one-half of the total 
area of France. Both in 1903 and 1904 the production of acorns 
was destroyed, and the rate of growth was seriously reduced, 
more especially on large and valuable trees, and Professor Henry 
estimates the loss at several millions of cubic feet in each year. 
Curiously enough, it also happened that the storm of 1st 
February 1902 damaged four sample-plots on which experiments 
had been commenced in 1892 to study the effect of thinning in 
silver fir-woods eighty-three years old, resulting from natural 
regeneration freed from the overhead shade of the parent stan- 
dards in 1840 to 1850, and thereafter thinned only to the extent 
of removing dead and suppressed trees. This interfered with 
the experiment just when it was becoming most interesting, 
but, all the same, useful results were noted on the fallen 
trees being worked up. Four sample-plots, of about 1} 
acres each, having been selected in two lots (1 and 2, 
3 and 4), similar as to soil and situation, one of each was 
thinned and the other left as it was, the standing trees being 
numbered and their diameter and height,registered. In 1899 a 
second thinning was made in plots 1 and 3, and an analysis of 
three of the wind-fall stems showed that although the growth in 
height had apparently not been much affected, the rate of growth 
in girth had been greatly increased at about 54 feet over the 
