56 Dr David Christison on the [sebs. li. 



Finally, it must be remembered that these conclusions 

 cannot be held to establish general rules, unless for trees 

 of similar age to those tested, and growing in similar soil 

 and climate. 



IV. The Months in which the greatest Increase of Girth occurs 

 ill Deciduous as distinguished from Evergreen Trees, 



In my former paper it was stated that the limited observ- 

 ations then available indicated July as occupying the first 

 place in the deciduous class, and June in evergreens. Sub- 

 sequent experience with the same trees confirms this ; but 

 as only a limited number of species have been tested, and as 

 some of them proved to be exceptions to the rule of their 

 class, it would be rash to found a general principle on such 

 a basis. Moreover, from observations begun in the present 

 year, I have reason to believe that a good deal may depend 

 upon the age of the trees experimented upon, and it is my 

 intention to test the whole subject more thoroughly by 

 additional observations on new species and younger sub- 

 jects. 



V. Proportional Monthly Increase in Girth of Different 

 Species of Trees. 



The two following Tables give the percentage of annual 

 growth due to each month in different species of deciduous 

 and evergreen trees. The figures I believe show accurately 

 enough the facts, so far as the trees actually under ob- 

 servation are concerned ; but certain reservations must be 

 used in accepting the results as establishing general laws of 

 growth for the several species concerned. 



In the first place, they are only applicaljle to the neigh- 

 bourhood of Edinburgh. Obviously very different results 

 may be expected from observations made under different 

 conditions of soil and climate, even within the limits of our 

 own island. 



Secondly, they are only applicable to trees of a certain 

 age. The great majority of the trees under observation 

 were between thirty and eighty years of age or upwards; but 

 experiments on young trees from 4 to 12 inches in girth, 

 initiated this year, lead me to believe that they, as a rule, 



