DEPARTMENT OF BOTANICAL RESEARCH. 45 



trees some time before enlargement of the trunk takes place. The 

 period separating 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. 



6. 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, how- 

 ever, 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 internode 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 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. 



7. The embrj^onic 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 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. 



8. Estimates of the range of daily equalizing variations in a Mon- 

 terey pine, taken from bearings on a thin layer of cork external to the 

 bast of a trunk which had ceased to grow for the season, show that 

 the diameter might vary 1 part in 1,750. That a large share of this 

 variation is due to changes in the hj^dration of the living cells is proved 

 by the fact that when bearings are taken on the woody cylinder of 

 the trunk internal to the growing layer the variation drops to 1 part 

 in 8,750 of the diameter. The actual change in volume, in the first 

 instance calculated on the basis of a conical trunk 18 meters high and 

 35 cm. in diameter at the base, would amount to about 400 cu. cm., 

 of which not more than one-fifth is attributable to variations in the 

 wood. It is to be noted, however, that the change in the volume of 

 the wood may by no means be taken to represent the water-deficit in 

 the wood. The woody mass is made up of box-like cells, which may 

 include a bubble of gas, the water forming no more than a thin film on 

 the wall of the cell and inclosing the gas bubble in the condition of 

 extreme water-deficit. The withdrawal of water through the walls of 

 the cells, which are semi-rigid, increases the surface tension of the gas 

 bubble, which results in a slight lessening of volume of the whole 

 mass, but in an amount that would constitute no more than a small 



