1921] KORSTIAN—DIAMETER GROWTH 459 
dependent upon temperature, and that soil temperature, insola- 
tion, and the thickness of the bark were influential factors also. 
GROSSENBACHER (3) has reviewed the varied and rather contra- 
dictory literature concerning radial growth in trees, the time of 
beginning and ending of cambial activity, and the factors thought to 
determine its distribution. He found a rather general agreement 
that, in our zone, wood formation generally ceases by mid-August, 
while that of the phloem continues practically to the end of the 
vegetative season. Hartic (5) concluded that cambial activity 
first began in the youngest twigs and then gradually proceeded 
downward. Hastincs (6) found that radial growth commenced 
first behind the opening terminal buds in broad-leaved trees and 
proceeded toward the base. By the time the five to six-year 
branches were forming new wood, radial growth had become 
general all over the trees. In the case of pine radial growth 
apparently commenced on the two or three-year old portions of 
branches before the buds opened. Growth started on the two- 
year pine branches possibly because the leaves were retained two 
years, for it was noted that in hemlock, where the leaves were 
retained six to seven years, radial growth appeared to have started 
first on six-year old branches. In Taxodium distichum radial 
growth started first just behind the opening terminal buds, as in 
broad-leaved trees, in which diameter increase did not begin until 
the buds had opened. REICHE (8) also noted that radial growth 
of trees in Chile began after the buds burst, and that it did not 
occur unless bud development preceded it. Buckuovurt (1) reported 
diameter increase in Larix europaea to be practically coincident 
with the formation of new leaves. 
Knupson (7), as a result of several years of investigation, 
including microscopical studies, found that the development of 
xylem in Larix laricina began a month later than the commence- 
ment of leaf formation, and ascribed BuckHovt’s observed diameter 
increase mainly to a preliminary swelling of the tissues. From his 
results and those of other investigators, KNUDSON believes it 
probable that in general diameter growth does not begin until the 
leaves have developed and have become sufficiently active photo- 
synthetically to supply the requirements of rapid cell formation. 
The reserve food materials stored up in the autumn are probably 
