DIAMETER GROWTH IN BOX ELDER AND 
BLUE SPRUCE 
C. F. KoRSTIAN 
(WITH THREE FIGURES) 
It is the common belief that trees grow throughout the greater 
part of the vegetative period, the commonly called “growing 
season,’ which is roughly defined as being limited to the period 
from the last killing frost in the spring to the first killing frost in 
the fall, when the broad-leaved hardwoods such as maple, ash, 
and aspen show their autumnal colors. In the Rocky Mountain 
forest region this period comprises from 75 to roo days. Until 
recently little was known as to the exact time at which trees 
actually make their diameter growth. Neither has the course of 
growth nor the formation of the annual rings or cones of wood 
been measured until recently. 
About twenty-five years ago Friepricw (2), an Austrian 
forester, devised instruments capable of measuring the daily 
growth in diameter of trees. Somewhat later he improved his 
accretion autograph, as it was called, by adding an electric attach- 
ment which recorded the growth in the investigator’s office. He 
would entertain his visitors by telling them that while they could 
not hear grass grow, they could not only see but hear the tree in 
the park grow, the increase in the periphery being announced by 
the sounding of a signal. 
In 1918 MacDoveat devised a new instrument for recording 
in minute detail the daily and seasonal growth and all changes in 
the size of the trunk of a tree. The instrument is called a dendro- 
graph. The essential part of it consists of a yoke composed of 
slotted bars of some alloy, such as bario or invar, which has a very 
low temperature coefficient. This is held in place by upright 
pieces of brass wire seated in small brass plates, which afford 
flexible supports capable of uniformly adjusting any tension which 
may be developed. These plates are clamped to a belt of wooden 
blocks hinged together and fastened securely to the tree, serving 
Botanical Gazette, vol. 71] [454 
