640 Harper . — Defoliation : its Effects upon the 
shows the ordinary zones of traumatic ducts that are formed year after 
year in the neighbourhood of injuries, such as the cankers caused by Peziza 
Wilkommii , and Fig. 16 shows a similar zone more Highly magnified. 1 
These ducts are very different from the irregular cavities shown in Fig. 17, 
which seem traceable in a more elementary stage of development in 
Fig. 18, from another part of the same tree. It may be pointed out that 
the phyllophagous larvae of the Sawfly can hardly cause any traumatic effect 
down in the trunk, and the ovipositor of the mature insect can only harm 
the tender shoots. Whether these abnormal resin-cavities are the result of 
an attempt to make normal ducts, in traumatic zones or otherwise, which 
has become abortive through declining growth-energy and lack of food, 
has not been decided. 
In conclusion, I wish to express my warmest thanks to Professor 
Somerville for the very ready way in which he put the resources of his 
laboratory at my disposal, and for helpful suggestions. I am indebted also 
to Professor Vines for facilities that were of great assistance in expediting 
the work, and to Professor R. W. Phillips, University College of North 
Wales, Bangor, for kindly criticism. The photographs were made from 
my own preparations and under my direction by Mr. Alfred Robinson of 
the University Museum. 
Summary. 
1. The material investigated was for the most part furnished by trees 
that had been repeatedly defoliated by larvae of the Large Larch Sawfly. 
2. Premature defoliation means a greater or lesser degree of starvation. 
3. Starvation affects both the quantity of the growth-increment and the 
structure of the wood formed. 
4. If starvation is severe, growth may quite cease over certain parts of 
the cambium- mantle while other regions of it are still active. Growth 
is especially reduced in the lower parts of the tree, where the rings are nor- 
mally narrower than higher up. Consequent on this regional inactivity of 
the cambium some rings may run only part of the way round a section of the 
trunk, or may even be wholly lacking. In larches killed by the defoliations 
growth ceased entirely at the base a year or more before the death of the tree. 
5. The effects of climatic variation have been negligible during the last 
few years, as far, at least, as some plantations are concerned. 
6. The first visible effects of defoliation in the structure of the wood is 
the reduction of the proper thickening of the walls of the cells of part or 
all of the zone of autumn wood, without much decrease in the breadth 
of the whole ring. Subsequent years may show quite normal autumn 
wood before the rings have recovered their former breadth. 
1 Cp. Tschirch, p. 1190 ; also Thomson, Figs. 1 and 2. 
