18 GROWTH IN TREES. 
tips of the branches, especially of young trees, begins about this time 
and such growth may continue until September, according to Dr. 
Forrest Shreve, who reports that records of elongation of as much as 
10 feet of the leaders of young trees are in existence. Dr. Shreve has 
also described the features of the trunk, but an example examined by 
the author will serve to illustrate the structure of such trunks. This 
tree was about 12.5 meters in height, 15 cm. in diameter a meter above 
the ground, and had 12 layers of wood in the heart and 18 in the lighter- 
colored sapwood. The heaviest increments to the trunk, according 
to Dr. Shreve, occur in the period of development between 10 and 20 
years of age, at which time very heavy layers of wood may be formed. 
Dendrographic measurements of the variations and growth of [the 
trunks of nine trees in the grounds of the Coastal Laboratory have 
been made since September 1918. A continuous record of the basal 
section of the large tree upon which the observations were begun has 
been kept since that time, and a second instrument was attached te 
this tree 9 meters above the ground in March 1920, so that a double 
record for an entire season is now available. 
The seasons in the region in which the Monterey pine grows are 
indeterminate as to frost and temperature features, but the rainfall 
occurs in the winter and growth is seen to depend upon the soil supply 
of water and the rising temperatures, with the result that enlargement 
of the trunks continues until the soil moisture around the absorbing 
roots is depleted until it forms no more than 6 to 10 per cent of the total 
weight. 
The present studies have been devoted chiefly to changes in volume 
of trunks and so many technical problems have been encountered that 
no attention has been paid to the features of development_of the cam- 
bium inclusive of the periods of cell-division, of xylem formation, of 
phloem formation and collapse, of rifts and stresses in bark, or seasons 
of activity of roots. Important contributions on these subjects have 
been made recently by L. Knudson,” H. P. Brown,’ and I. W. Bailey.* 
It was thought advisable, however, to make some measurements of 
the changes in length and thickness of leaders and young stems and 
this was done both in the early part of the season and in the autumn. 
1 Shreve, Forrest. Stem analysis and elongation of shoots in the Monterey pine. Carnegie 
Inst. Wash. Year Book for 1919, pp. 88 and 89. 
2 Knudson, L. Observations on the inception, season, and duration of cambium development 
in the American larch (Larix laricina Du Roi Koch). Bull. Torr. Bot. Club, 40: 271-293, June 
1913. 
3 Brown, H. P. Growth studies inforest trees. I. Pinus rigida Mill. Bot. Gaz., 54:386-402, 
1912. II. Pinus strobus L. same journal, 59: 198-240, 1915. 
4 Bailey, I. W. Phenomena of cell-division in the cambium of arborescent gymnosperms and 
their cytological significance. Proc. Nat. Acad. Sci., 5: 283-285, 1919. 
. The cambium and its derivative tissues. II. Size variations of cambium initials in 
gymnosperms and angiosperms. Amer. Jour. Bot., 7:355-367, 1920. ILI. A reconnaissance 
of cytological phenomena. Amer. Jour. Bot., 7:417-434, 1920. 
