246 Dr Christison on the [sess. lii. 



effect of this has, no doubt, been to unduly depress many 

 of the averages, and to prevent us fi^om accepting this 

 decennial period as representative of decennial periods in 

 general. 



These two disturbing elements have gi'eatly complicated a 

 subject which otherwise might have been simple enough, and 

 in the sequel I shall have constantly to point out their effects 

 in modifying or annullmg the value of results in trees or 

 even in whole species. 



In presenting the numerous and somewhat complex results 

 arrived at, the method I have adopted is, first to give 

 a tolerably complete history of each species separately; 

 secondly, to give comparative results and general conclusions 

 derived from this record of facts. It is to the first of these 

 divisions that the present paper is confined. 



At the outset it is necessary to explain certain rules 

 canied out through the work for convenience and economy 

 of space. 



1. The girth of a tree invariably signifies the girth of the 

 stem at its narrowest part within easy access, which is 

 generally about 5 feet from the ground. 



2. All measurements are in inches and decimal parts of 

 an inch, unless otherwise stated. 



3. Trees at Craigiehall are distinguished by an asterisk 

 from those in the Botanic Garden. 



PAET I. 



GENERAL HISTORY OF THE SPECIES THROUGH THE 

 DECENNIAL PERIOD. 



The chief points to be considered in tliis Part are the 

 general condition and progress of the trees and species ; 

 their average annual increase ; the annual range of their in- 

 crease ; and their share in the depressions wliich occurred in 

 1879-80-81, 1883, and 1887. Only the first of these de- 

 pressions is treated in detail in this Part, as its effects were 

 so great and general. Tiie share taken by the species in the 

 other depressions will be more conveniently considered in 

 the Second Part. 



