lod 
THE VERTICAL GROWTH OF TREES. 319 
found to be nearly covered by the bark. The results of 
these observations go to show that the extension of the 
stem is made at the summit or growing point of the plant, 
and not between the branches. 
It is difficult to always guarantee the accuracy of the 
measurements nearer than to half an inch. Where the 
tree grows perfectly straight and the measurements are 
taken froma nail driven into the base of the stem, and 
there are no branches in the way, a high degree of accuracy 
can be maintained. An objection to measuring from a peg 
is that as the tree grows, the peg gets pushed out of 
position, so that it is considered better to start the measure- 
ments from a base-nail. Hxtreme accuracy is difficult to 
obtain if the tree becomes crooked, or grows out of the 
perpendicular. ! 
In the following tables the first column indicates the 
number of nails, one foot apart, driven into the stem on a 
given date, and also the number of branches between each 
nail. The remaining columns show the measurements to 
each nail on subsequent dates, and the number of branches 
then remaining, there being practically no difference found 
in the position of the nails in the great majority of cases. 
The columns also show where higher nails have been placed 
as the stems increased in height. 
The diameter of the stem was measured at two feet from 
the ground in all cases. Asa general rule the top of the 
plant was about one anda half feet above the highest nail, 
and this higher portion of the stem was too frail to admit 
of a nail being driven into it. 
1 For information concerning the increase in diameter of ordinary 
timber trees, see a paper entitled “Growth of Trees, with a Note on 
Interference Bands formed by Rays at Small Angles,” by A. Mallock, F.r.s. 
Proc. Roy. Soc., London, Series B, Vol. 90, No. B 627, (1918). 
