630 Harper . — Defoliation: its Effects upon the 
Owing to the denseness of the plantations the crowns of these larches 
would be restricted in development, and down the bare trunk below the 
lowest of the branches the growth-intensity, and with it the £ Flachenzuwachs 
would steadily decrease towards the base of the tree. Now if as one gets 
nearer and nearer to the base the whole sectional area of the annual ring 
is becoming less, while at the same time the circumference is steadily 
increasing as the thicker parts of the trunk are reached, it is clear that the 
breadth of the ring must decrease in a very striking manner, as is shown by 
Table I for a larch that had never been attacked by the Sawfly, and which 
may therefore be taken as a standard of comparison for the others. In the 
column showing the average ring-breadth for the last six years there is 
a regular gradient from section to section except at two points only. One 
of these is at the very base of the tree (section 1), at the root-stock in fact, 
where, as has been said, exceptional growth is to be expected. The other 
is in the topmost section, from the uppermost part of the crown, where the 
annual increment falls off again very rapidly according to the rules already 
mentioned. 
The reasons why growth varies in different parts of the tree cannot be 
dealt with at length in this paper. Various explanations have been put 
forward. Schwarz 1 would refer the matter to differences in the longitudinal 
pressures acting on the cambium, these varying inversely with the strength of 
the wind’s leverage at any part of the trunk and the capacity of resisting this 
bending force. Hartig 2 seeks a sufficient cause in supposed differences in 
the distribution of carbonaceous food-materials, mineral salts, of soil and air 
temperatures, &c. The facts themselves are enough for the present, and 
indeed a single satisfactory explanation of them has not yet been suggested. 
These facts of distribution and localization of growth-intensity in 
normal trees have an important bearing on cases where the vitality has 
been lowered through defoliation or other causes. For when growth is 
reduced it will naturally cease first where it is normally least. In stunted 
trees, for instance, rings which fail close to the base may reappear in the 
root-stock, the growth there being normally greater than immediately 
above it. 3 The narrower rings, therefore, may be altogether absent from 
the base of the tree, though at the top it is still possible to count back ring 
by ring to the year of the commencement of the attack or depression of 
growth (see Tables IV, VI, and VII). Or at the base, again, a ring that is 
feebly developed may only reach part of the way round the tree (Fig. 6), 
though it may be complete higher up. £ Partial rings,’ in fact, may arise 
over very small arcs of the circumference, only small circumscribed patches 
of the cambium mantle being active (A in F'ig. 7). These partial rings 
are quite distinct from the ‘ multiple rings ’ that are occasionally found in 
larch and other trees, where at first sight several rings appear to have been 
1 Schwarz, pp. 2 and 160. 2 Hartig (8),p. 271. 3 Cp. Schwarz, p. 213. 
