Dec. 1897.] BOTANICAL SOCIETY OF EDINBURGH 89 



nature become historic, and do not occur often enough to 

 account for the variation. 



Other meteorological conditions, however, must be taken 

 into account, since they form some of the factors which 

 determine the growth of all plants ; these are temperature, 

 moisture, and sunshine. The relationship of these factors 

 to the annual increment of girth will form the subject of 

 a second paper. 



The following were our methods of examining each 

 tree : — After choosing an evenly-sawn section close to the 

 ground, we found its orientation by means of a pocket 

 compass, then cut two smooth tracks on the surface with 

 a wood chisel so as to get N. and S., and E. and W. 

 diameters, each passing through the pith. 



The total lengths of each diameter, and each radius, 

 were measured by us in turn, while the other noted the 

 measurements on paper ; then the breadth of each annual 

 ring was taken with a steel millimetre measure, and these 

 measurements were checked at every tenth year. 



It must be understood that the measurements were 

 made of the wood only, and did not extend beyond the 

 cambium. 



When the annual rings of the first few or the last years 

 of a tree were too close for accurate individual measure- 

 ment, a collective number was measured. 



Specimen A was thus measured collectively for the 

 first 6 years ; B for the first 5 ; D for the last 30; U, -F, 

 and G had every annual ring measured along each of the 

 four radii ; H had a few collective measurements taken 

 between the ages of 25 and 50 years. 



The sections were immediately above the ground-level, 

 except — D, 12 feet above ground; F, 32 feet above 

 ground; and II, 34: feet above ground. 



It would have been better to have got sections 4 or 

 5 feet above ground, so as to be away from the buttressed 

 part of the trunks near the roots ; but we had no 

 choice, since we had to examine the sections as we found 

 them. 



In calculating the girth for any one year, the increments 

 of the four radii of that year are added to the sum of the 

 radii of all the preceding years ; the total is divided by 2 



