272 KNUDSON: CAMBIUM DEVELOPMEMT IN AMERICAN LARCH 
activity began from two to four weeks later in the lower part of 
the trunk than in the twigs. 
Asa result of extensive investigations, Robt. Hartig* advanced 
the idea that cambial awakening was dependent upon temperature 
and that therefore the thickness of the bark, temperature of the 
soil moisture, and insolation, were important factors. He found 
in an isolated 10-year old Pinus sylvestris, that cambial activity 
had begun two weeks earlier than in isolated 35- and 65-year old 
trees, and four weeks earlier than in a 1o0-year old tree grown 
under forest conditions. The comparisons were all made at a 
height of 6 meters. He also found that under natural forest 
conditions the growth of the annular ring of Scotch pine, Norway 
spruce, and European larch at a height of 27.5 meters, was on 
June 9 respectively 66 per cent, 56 per cent and 75 per cent 
completed. Going toward the base the growth decreased, and 
at a height of 1.5 meters the percentage of the annular ring com- 
pleted was 35, 21 and 18 per cent respectively. In isolated trees 
of Scotch pine and Norway spruce the growth on July 9 was ap- 
proximately the same in all parts of the trunk. Under forest 
conditions growth was found to begin in the twigs and proceed 
downward, the cessation of growth following the same order. 
According to Mer,} the cambial activity in oak, beech, bass- 
wood, fir, and other trees of twenty-five years of age and under 
begins in the youngest twigs. In older trees cambial activity 
is described as simultaneous at the bases of the branches and 
trunk. He states also that in a single cross-section cambial 
activity may be evident on one side and not on another. 
Hastings} found that in broad-leaved trees increase in diam- 
eter did not begin until the buds had opened. He found that 
growth first begins in the 1-year old twigs, and later it occurs in 
2- and 3-year old twigs. When wood is forming in 5- or 6-year 
old growth there is simultaneous development over the entire 
tree. In pine it begins first in the 2- and 3-year old twigs. In 
the hemlock the growth was first observed in the 6-year old twigs, 
* Hartig, R. Das Holz der deutschen Nadelwaldbaiume, 35-38. 1885. 
{t Mer, E. Sur les causes de variation de la densité des bois. Bull. Soc. Bot. 
France 39: 95-105. 18092. 
t Hastings, G. When increase in thickness begins in our trees. Science II- 
12: 585. 1900. 
