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 
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 
1JIt 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. 
