DEPARTMENT OF BOTANICAL RESEARCH. 77 



If the data obtained from plantlets, from young trees, and trunks of 

 mature trees be taken to apply to the corresponding parts of a large tree, 

 a composite picture is obtained in which the growing tips and trunks 

 are seen to be growing most rapidly at night or on foggy days, the stems 

 1 and 2 years old enlarge during the midday period, and the trunks 

 shrink during this same period, indicative of a mechanism which may 

 be of importance in the ascent of the sap. 



The Growth of an Oak Trunk, by D. T. MacDougal. 



A dendrograph with a U-shaped yoke of bario was attached to the 

 trunk of an oak {Quercus agrifolia) 35 cm. in diameter, standing near 

 the main building of the Coastal Laboratory at Carmel, California, 

 on February 17, 1919. The system w^as arranged to give an ampli- 

 fication of 12 and temperatures were taken by a mercurial thermometer, 

 the bulb of which was thrust in a hole prepared for it to a position 

 between the bark and the wood. The meteorological record was also 

 kept. 



Actual growth began on the afternoon of March 10, about a week 

 before nevv' leaves began to unfold on this tree, although some had 

 been formed on other individuals of the species in the vicinity. The 

 temperature of the trunk ranged from 9° to 14° C. Enlargement, with 

 interruptions of a day or a few days, continued until August 5, a total 

 period of 148 days, in w^hich time the total increase in diameter of the 

 trunk and bark was 6.2 mm. The bark of this oak remains alive 

 until the trunk reaches some size and has a complete external layer 

 upon which the contacts are made directly. The layers immediately 

 beneath are chlorophyllose. Three large rifts formed previously in the 

 lower part of the trunk widened irregularly, as shown by variations in 

 the record, in which the deformations due to wind action on the 

 crown are also discernible. Periods of retardation or cessation of 

 growth and of shrinkage were coincident with conditions of low 

 humidity and high temperature making for excessive water-loss. 



Growth of Beech and Sycamore Trees, by D. T. MacDougal. 



A dendrograph w^as attached to a beech tree {Fagus grandifolia) 

 in the grounds of Johns Hopkins University, Homewood, Baltimore, 

 in mid-April, under the care of Mr. W. F. Gericke. Some enlargement 

 was discernible on May 12, immediately upon the attainment of full 

 foliage. Enlargement continued at a low rate during the remainder of 

 this month, June, and July. During the latter part of July the rate 

 was especially high. Enlargement continued until about October first. 

 The daily variation did not amount to more than 0.3 or 0.4 mm., 

 being of the type of the live-oak at Carmel, representing the action of 

 trunks with living bark, from which direct water-loss is much less 

 marked than in the case of the pine and ash. 



