Exotic Conifers in Britain. 



343 



incredible result that 7,433 cubic feet of wood' have been added 

 per acre during the past fifteen years, an average increase during 

 that period of 495 cubic feet per acre per annum. When, 

 however, it is seen that even the smaller of the two sample 

 trees contains about three times as much timber as the sample 

 tree of 1888, and bearing in mind the fact that no trees have 

 been removed since that year, the result becomes more easy of 

 credence. 



During the same period the average height has increased 

 from 60 to 83 feet, the point of 3 inches diameter being reached 

 at 48 feet in 1888 and 75 feet in 1903. 



Taking the age of the wood (forty-seven years) from the 

 time the seed was sown (1856), we have a mean height-growth 

 of 177 feet per annum, and a mean annual increase in volume 

 per acre of 238 cubic feet. 



The contents of the two sample trees are calculated both 

 as to true contents and also by the English system of quarter- 

 girth measure. In the case of No. 1, the true volume was 

 58*93 cubic feet, while the quarter-girth contents were 46*76 

 cubic feet, so that to reduce the former to the latter it is 

 necessary to deduct 20*65 P er cent. ; while to convert quarter- 

 girth measure into true contents, it is necessary to add 26*03 P er 

 cent. 



In the case of tree No. 2, the corresponding percentages 

 are 21*41 and 27*25. For ordinary purposes, therefore, it will 

 suffice to add a fourth in converting quarter-girth contents 

 into continental or calliper measure ; while to convert the 

 latter into the former a fifth must be deducted. Dr. Schlich's 

 sample tree contained about 14 cubic feet quarter-girth measure, 

 so that an acre carried — 



14 X 202 = 2,828 cubic feet. 



The smaller of the sample trees measured this year contained 

 39*42 cubic feet by the same system of measurement, there- 

 fore — 



39*49 x 202 = 7,977 cubic feet per acre. 



In 1888 Dr. Schlich calculated the "form figure" of the Douglas 

 fir at the age of thirty-two years to be -39, and anticipated that 

 it would gradually decline.* This, however, has not proved 



* Loc. cit. p. 237. 



