6 GROWTH IN TREES. 
Monterey pine (Pinus radiata) shows beginning growth of the trunks 
with the advance of temperatures, January to April, and comes to 
rest in July with the desiccation of the soil. Quercus agrifolia in the 
same region begins earlier and ceases to grow in June or July. Both 
may be awakened in July or August by deep irrigation of the soil. 
7. The trunks of all the trees measured show a daily variation in 
size, by which the maximum is reached shortly after sunrise and the 
minimum at a time after noon, dependent upon external agencies. 
These variations appear to depend upon the water-balance in the 
woody cylinder, are greatest in the seasons in which water-loss from 
the crown is greatest, are least in the cooler or damper seasons, and 
are to be detected in the records even in the period of most rapid 
enlargement of the trunk. 
8. Measurement of variations in the woody cylinder were taken by 
arranging the contact rods of the dendrograph to bear on the wood 
formed by the tree two years previously. Thus, in 1920 holes were 
bored through the wood of that year and of 1919 and contacts made 
at the bottom of the cavities. 
9. In general the awakening and growth of the terminal buds with 
resultant elongation of leaders and branches begins in many trees some 
time before enlargement of the trunk takes place. The period sepa- 
rating the two may be no more than a week in Quercus agrifolia 
and has been seen to be as much as 10 or 12 weeks in Pinus radiata. 
Observations on the Parry spruce and Douglas fir show that the trunks 
of these trees are enlarging at a time when the buds are in a very 
early stage of enlargement. 
10. In the single case in which dendrographs were attached to a 
pine tree 1 meter and 8 meters above the ground, growth began coin- 
cidentally at the two places in 1920. In the following year, however, 
the dendrograph at the higher point on the trunk recorded enlargement 
a few days before any action near the ground was made visible. In 
February 1921 an auxograph was brought into bearing on the inter- 
node of a pine tree 5 or 6 years old which had been formed in 1919. 
The buds had made a growth of 4 or 5 cm., but no action had yet 
begun in the internode. A second instrument was brought into 
_ bearing on the middle of the internode formed in 1920 on another young 
tree. Steady enlargement was in progress. 
11. The embryonic layer of a tree is in the form of an inclosing sheath 
terminating in the cones of the growing points. Activation of this 
tract is generally initiated in the growing points. Swelling in the 
cambium layer may be practically coincident with this awakening in 
some trees. Cases are recorded in the present paper in which weeks 
elapsed between the awakening of the buds and the enlargement 
of the base of the trunk. Activation of the growing cells may be taken 
to depend upon the localized food-supply, temperature, moisture, or 
other factors. ; 
