4 GROWTH IN TREES. 
increase of the volume of the protoplasm and an enlargement of the 
cell-mass of which it forms a part. 
Any instrumentation of sufficient accuracy and delicacy to measure 
the increases or variations due to growth in the cambium layer will at 
the same time include the variations in volume of the woody cylinder, 
which is also the conduit through which liquid passes from the roots 
to the crown. Similar conditions prevail in nearly all higher plants, 
and growth measurements of all stems, leaves, and roots include 
changes in woody or non-living cells. 
Such trees as the birch, with 200,000 leaves, are reputed to transpire 
as much as 400 liters in a single day. No estimates of the pines are 
available, but the low moisture content of the soil around the roots of 
the Monterey pine would not furnish a supply for such use of water. 
The trunk of a tree may, in fact, be compared to the supply hose of a 
fire-engine coupled to a hydrant. When the pressure from the mains 
is enough to supply water faster than it can be pumped out, the hose is 
distended. When the engine tends to take water faster than it would 
be delivered by the system, the hose would tend to collapse. Some- 
thing of this sort takes place in many trees which have been kept under 
observation. The conduit in this case, however, is not a simple pipe 
or a set of pipes, but is made up of vessels, through which water may 
pass under capillary conditions, and inclosed box-like tracheids which 
may be only partially filled with water. When water is withdrawn 
from such a system faster than it is taken in, the resulting changes in 
form and size are complex in character. 
These facts were well considered in my experiments previously 
carried out when the measurement of growth in trees was taken up 
in 1918, and a new technique with specially designed instruments 
was found necessary for the analytical study of the changes in volume 
of these massive organs. The records are now continuous for a large 
number of trees for many months, one tree having been under con- 
tinuous measurement since September 1919. The chief features 
considered in the present paper are as follows: 
1. The dendrograph, an instrument for making continuous records 
of the variation of tree trunks, has been developed to an approximately 
final form.'' The essential feature of this instrument consists of a 
floating frame of metal of low temperature coefficient, such as invar 
or bario, which may be placed around a tree trunk, and the variation 
IMacDougal, D. T. The dendrograph: a new instrument for recording growth and other varia- 
tionsin the dimensions of trees. Carnegie Inst. Wash. Year Book for 19 18, pp. 59-60. 
. ae dendrograph. Carnegie Inst. Wash. Year Book for 1919, pp. 72-78. 
‘ he course of growth in trees as measured by the dendrograph. C i 
Wash. Year Book for 1920, pp. 51-52. hes sa a 
. Measurement of a season’s growth of trees by the newly designed d 
Carnegie Inst. Wash. Year Book for 1920, p. 52. me saab 
A brief discussion of the contents of the present paper was given before the A i 
ZEgeopnisal Society at Philadelphia, April 22, 1921, which is in press in the Henne 
the Society. ; 
