378 R. H. CAMBAGE. 
anything to corroborate this observation, old blazes and 
shields on marked trees having senor aay been found at 
about the usual heights.* 
Some years ago Mr. District eae W. M. Thomas 
drew my attention to the results of some tests made by 
Mr. G, W. Cooley, in America, in regard to the stability of 
bench marks cut near the base of fifteen trees of several 
different species.2, The observations extended over a period 
of five or six years, the tests being made annually. No 
upward growth was detected, although a change from one 
to three-hundredths of a foot was noticed from year to 
year, probably caused by the action of frost during the 
winter. 
It was further pointed out that three nails driven into 
some of the trees, about four feet above ground, maintained 
for five years the same relative position with regard to the 
nails on the bench marks. It may be mentioned that the 
trees selected for use as bench marks in the above tests 
were from three to twenty inches in diameter, the majority 
being one foot and upwards, and it might seem more reason- 
able to expect an extension, if any, to take place in such 
trees in the higher rather than the lower portions of the 
boles. 
Some experiments have been carried out by me for years 
past on very young trees growing in my own garden, and 
in the Sydney Botanic Gardens, the latter tests being made 
by permission of the Director, Mr. J. H. Maiden. These 
tests have been made by placing small tacks in the stem, 
one foot apart, the measurements being taken from a peg 
driven into the ground, or in some cases from a nail driven 
into the base of the stem. Tacks were renewed when 
1 The Surveyor, xvii, 226, (1904). 
2 Trans. Amer. Soc. Civil Engrs., xx, 73, (1889). The Surveyor, XviIt 
35, (1905). 
