Growth and Structure of the Wood of Larix. 629 
Sawfly larvae is the striking absence of the strongly thickened tracheides that 
usually occur as the zone of ‘ autumn wood ’ at the close of the year’s growth 
(PL XLIX, Figs. 1, 2, and 3). At first, perhaps, there is no significant decrease 
in the ring-breadth itself, but subsequent years show much narrower rings, 
with, however, in some cases a fair proportion of normally thickened autumn 
wood (Figs. 1, 2, and 4). It is this absence of thickened cells from the first 
ring to show the attack that gives the date of subsequent rings in those 
parts of a tree where the cambium has ceased to function a year or two 
before the trees were felled. For, as will be mentioned later, some of the 
trees ceased growth at the base of the trunk while they still formed rings 
year after year in the crown. In the crown there is a ring formed every 
year till the death of the tree, so, counting from the first ring to show no 
autumn wood at the top of the tree, it is possible to compare any subsequent 
ring with the corresponding growth for the same period lower down the trunk. 
As might be expected, these starvation effects are most in evidence 
towards the base of the tree, for there the growth is normally less energetic 
than up in the crown. But the ring-breadth itself cannot be taken as 
a measure of comparison of the growth intensity at different heights up the 
trunk, since the circumference is of greater or less extent according as the 
section is taken close to or far from the ground. The ring-breadths in these 
tables are given for a comparison of the growth in different years at the same 
height, not that of the same year at different heights. For comparing the 
amount of growth at different heights the superficial area of the whole ring in 
cross-section of the trunk would be required, the ‘Flachenzuwachs’ of German 
foresters. This ‘ Flachenzuwachs ’ varies in different parts of a normal tree 
according to definite rules. 1 In the crown, for instance, the * Flachenzuwachs ’ 
increases the farther down one gets from the top, but in the branchless part 
of the trunk it usually decreases steadily towards the base, where it suddenly 
increases again to form the so-called ‘ root-stock \ If the tree grows alone 
in the open its lower branches do not drop off, and the tree is consequently 
all crown. Physiologically, at least, it is in a similar condition if through 
the felling of its neighbours it is relieved of competition and placed in 
circumstances exceptionally favourable to energetic assimilation. In either 
case the growth-intensity, as measured by the actual growth-increment or 
‘ Flachenzuwachs steadily increases from the top right down to the base 
of the tree. The larches investigated, however, all came from dense planta- 
tions, but those from which Tables V, VI, and VII were derived had been 
left somewhat isolated by a severe thinning in the years 1909 and 1910. The 
apparent recovery shown in 1911 in tree D and the upper parts of trees E 
and F (Tables V, VI, and VII) is probably due to the increased illumination 
to which they were thereby exposed (cp. the outermost ring in Fig. 1 with 
that which immediately precedes it). 
1 Cp. Hartig (2), and Nordlinger. 
