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, 1 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 batal 

 section of the large tree upon which the observations were begun has 

 been kept since that tune, and a second instrument was attached to 

 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, 2 H. P. Brown, 3 and I. W. Bailey. 4 



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. 



1 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. 



* Brown, H. P. Growth studies in forest trees. I. Pinus rigida Mill. Bot. Gaz., 54: 386-402, 

 1912. II. Pinus strobiu L. same journal, 59: 198-240, 1915. 



* Bailey, I. W. Phenomena of cell-division in the cambium of arborescent gymno^perms 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. III. A reconnaissance 

 of cytological phenomena. Amer. Jour. Bot., 7:417-434, 1920. 



