Defoliation : its Effects upon the Growth and Structure 
of the Wood of Larix. 
BY 
ALAN G. HARPER, B.A., 
Demonstrator in the School of Rural Economy , Oxford . 
With Plates XLIX and L and two Figures in the Text. 
Introduction. 
T HE larch trees investigated had been defoliated for several years in 
succession by larvae of the large larch Sawfly (Nematics erichsoni). 
This pest, which since 1882 has killed nearly every larch in the Adirondacks, 
was suddenly reported from the English Lake District. The first mention 
of its presence was in September, 1906, in a memorandum of the Board of 
Agriculture reporting damage done by it there during that summer. It 
had begun its ravages there, however, as early as 1904, 1 and was reported 
from Wales and Ayrshire in 1907. Since then it has done an enormous 
amount of damage to larch plantations in the Lake District and in Wales, 
and in 1910 it was scheduled under the Destructive Insects and Pests 
Order of the Board of Agriculture and Fisheries. Not only the European 
Larch, but also the more recently introduced Japanese species (Larix 
leptolepis) is attacked. The nature of the damage is as follows: the 
larvae, emerging in early June from eggs laid a week earlier in the cortical 
tissues of the terminal shoots of the branches, work their way down towards 
the main trunk, eating every leaf as they proceed. In three or four weeks’ 
time they drop to the ground to spin cocoons in the moss, leaving the tree 
completely or in part defoliated and with the terminal shoots in which the 
eggs were laid withered. Sometimes, however, a second flush of leaves is 
produced upon the spur shoots towards the end of the summer, but these 
are liable to injury from early frosts. The cocoons hatch out next May, 
and the process may be repeated year after year until the tree becomes 
weaker and weaker and ultimately dies for lack of nourishment. 2 
In so far as its green leaves are the seat of photosynthesis their 
untimely removal must affect the food supply of a plant. In spring, when 
the winter buds of trees unfold, the plastic reserves, stored up during the 
preceding summer, are drawn upon not only for the material of the leaf 
tissues itself, but also to keep up the active metabolism necessary for 
supplying sufficient energy or osmotic substances necessary for the actual 
expansion of the growing cells. That the source of this growth-energy is 
1 MacDougall. 2 For further details cp. the papers of MacDougall, Hewitt, and Annand. 
[Annals of Botany, Vol. XXVII. No. CVIII. October, 1913.] 
