78 CHRISTISON—OBSERVATIONS ON 
that the severe seasons of 1879 and 1880 produced, besides an 
immediate severe depression, a permanent effect, by accelerating, 
or it may be in some cases inducing, the falling off in girth 
increase to be looked for in trees either beyond their prime or 
in weak health ; and this took place in the majority without any 
apparent degeneracy in the foliage. In the two Limes and the 
Sycamore it has always been fine, and the same may be said, in 
a somewhat less degree, of the Spanish Chestnut, Tulip Tree, and 
Hornbeam. The conduct of the Horse Chestnut was peculiar. 
It probably rallied completely in 1881 from the previous severe 
seasons, but in 1882 fell a victim to some disease that withered 
the foliage early in summer of nearly all the Sycamores near 
Edinburgh, and, although subsequently the foliage was always 
healthy and dense, the girth-increase for fifteen years has been 
very slight,and in some seasons there has been none at all. Per- 
manent injury to girth-increase, if it existed at all, is least 
traceable in the Hornbeam and American Oak. In the Walnut 
and Birch the degeneracy both in appecers and girth-increase 
is distinct. 
E. Variety in the Incidence of Years of Depression on the 
Different Species. 
This is perhaps most simply shown by the following state- 
ment :—Of the nine species in twenty years, 4 were affected in 
1879, 8 in 1880, I each in 1881, 1882, and 1883, 2 in 1885, 2 in 
1887, 3 in 1888 and 1889, 5 in 1891, 2 in 1894, 4 in 1895, I in 
1896, and 8 in 1897. 
F. Capacity of Girth-increase as shown in Favourable Years. 
To show the growth accomplished by trees of the different 
species under favourable circumstances I have drawn up Table 
VII. From this it appears that Sa/zx stands, in a most marked 
degree, at the head with an average increase of practically three 
inches, and a maximum increase in a single year of four inches, 
the average girth being nineteen inches. In the four best con- 
secutive years it grew fully a foot in all. No other tree comes 
up to this, but Quercus conferta comes next with an average for 
five consecutive years of above an inch and three-quarters, and 
Ulmus montana is third, with a little below that amount, the 
