GROWTH IN TREES. 9 
This ingenious method would enable the observer to detect changes 
of 0.00005 inch in circumference, but as no recording devices are 
provided the constant attendance of the observer was necessary. 
Meanwhile my own results show that an actual amplification of 8 to 
15 times the changes in diameter of the trunk is adequate for direct 
observation and analysis. 
Friedrich had previously used a device for recording increments to 
the thickness of trees as early as 1905.1 The tree was encircled 
with a steel band on roller bearings, and the ends were attached to 
both registering and recording arms. No cognizance was taken of 
errors due to changes in temperature, and no results obtained with 
this apparatus have been seen. 
Some success having been attained in the measurement of the varia- 
tions in stems such as those of the sunflower (Helianthus) and in the 
variations in volume of succulent stems such as those of Opuntia, 
by the use of mechanical levers, it was found desirable to extend the 
observations to trees. It was thought that accurate measurements of 
the changes in volume of these massive structures might not only 
give information of value on the subject of hydration and growth, but 
that some light might be thrown on the problem of ascent of sap. 
The attempt to measure the variations in large trunks, begun in 
1918, raised many difficult mechanical problems. First it was obvious 
that it would be practically impossible to hold the stem of any but 
small trees rigidly in any position. This made it necessary to devise 
means whereby the tree would support the instruments and carry 
them with it as it swayed and leaned. It soon became evident that 
such an appliance should consist of two parts; a base which would 
remain firmly in whatever position near the horizontal it might be 
placed about the trunk, and which would carry the more delicately 
arranged members of the second part which would register variations in 
diameter at some little distance from this base. 
Two forms of base or support were devised and tested. One form 
consisted of a rectangular frame built up of bands of wrought-iron 
2 by \% inches and of oak wood 2 by 2% inches, which could be 
clamped about the tree tightly by means of an iron rod, including a 
heavy turnbuckle. A heavy block of seasoned oiled wood at one end 
formed a base for the levers and recorders and a wooden screw 30 cm. 
long, working in a smaller threaded block hinged to the outer end of 
the larger base block, extended to a point on the trunk several centi- 
meters below and formed a brace which kept the block rigid in its posi- 
tion with respect to the tree. Flexible supports carried a floating 
frame which served to register variations in thickness. This form of 
base was heavy, unwieldy, and by reason of the metal was subject to 
temperature variations which might influence the record. 
\ Friedrich, J. Zuwachsautograph. Centralb. fir das gesammte Forstwesen. 31, pp. 456- 
461. Nov. 1905. 
