GROWTH IN TREES. 15 



Actual adjustment of an instrument in this manner is a work of about 

 an hour. During all of this time the recording lever has been kept 

 in a vertical position. It is now lowered until the short arm engages 

 the guide on the quartz rod and is in good contact. The recorder is 

 now swung around until the paper on the drum is brought against the 

 pen, being rotated to begin tracing on the proper day and hour. With 

 pens properly inked, a complete record for a week may be obtained 

 without further attention. 



Not all of the results cited were obtained with the instrument de- 

 scribed above, which has been in use only since September 1920, but 

 the earlier records have not been used in any manner in which their 

 faults might vitiate the general discussions and conclusions founded 

 on them. 



THE DENDROMETER. 



The records made by the dendrograph show the volume or diameter 

 of the tree at any moment and the variations which have taken place 

 in reaching these dimensions. Such observations are indispensable 

 to any searching study of the course and physical basis of the growth 

 procedure. It is also important to determine the total amount of 

 growth which may have taken place in a trunk during a season or a 

 period of years. Such an instrument would serve to check the detailed 

 records of the dendrograph and would have direct usefulness in the de- 

 termination of the increment in trees grown for timber. 



An instrument of this kind, which might be read only at the be- 

 ginning or end of a season, could be constructed of common materials 

 without regard to the temperature coefficient of the members Such 

 an instrument, known as a dendrometer, was designed in 1920 and a 

 number of models have been in attachment to trees since May of that 

 year. 1 



The principle of an encircling wire carried by a number of plungers, 

 originally tested for the dendrograph in 1918, was utilized in the 

 construction of the dendrometer. Such a device was unsuitable for 

 the recording instrument, as it was impossible to secure a wire of 

 sufficient flexibility with a low temperature coefficient. As noted, how- 

 ever, this objection had no weight in the simpler instrument, which 

 was to be read at long intervals. The first assembly of this instru- 

 ment, consisting of a belt of blocks linked with strips of galvanized 

 iron 125 mm. long, 40 mm. wide, and 0.8 mm. in thickness, bearing 

 guides for five radially arranged plungers, was fastened to a Quercus 



1 It is to be noted that the term dendrometer has been applied to instruments used by the 

 forester by which the diameter of trunks is taken by direct observation, the observer sighting at 

 the part of the trunk to be measured. See D. Bruce: A new dendrometer, Univ. of Calif. Pub., 

 3, No. 4, pp. 55-61, 1917. 



