50 SIR ROBERT CHRISTISON AND DR CHRISTISON ON THE 



II. Monthly Observations. 



* Encouraged by the results of his annual measurements, Sir Robert 

 Christison selected in 1880 five deciduous and six evergreen trees, already- 

 ascertained to be quick growers, as suitable for monthly observations. These 

 trees comprised two beeches, three Hungary oaks, four Sequoias, one Araucaria, 

 and an African cedar. They were measured at the end of May, June, July, 

 August, and September. The operation was repeated by himself in the same 

 months, with the exception of May, in 1881 ; and again by me in 1882, 

 with the exception of August. Thus a tolerably complete record of the 

 monthly increments of these trees was obtained for three seasons. As the 

 number experimented upon, however, was both too limited and comprised too 

 few species to give altogether reliable results, I commenced in 1882 to make 

 monthly measurements of a considerably larger number, and henceforth twenty- 

 eight- deciduous and eighteen evergreen trees, including twenty-two species, 

 will be under observation. 



I shall now proceed to consider the conclusions to be derived from these 

 measurements in the solution of the following questions : — 1, What are the 

 months to which the groivth of wood is confined (a) in deciduous trees as a class 

 and (b) in evergreens as a class ? 2. In which month is the groivth of wood 

 most active in these two classes (a and b) respectively? 3. What are the 

 peculiarities in these respects of different species of trees f 



In the Tables III., IV., and V. the facts will be found in detail on which 

 the subsequent conclusions are founded. Table III. gives the three years' 

 measurements and average growths of the smaller number of trees originally 

 selected by Sir Robert ; Tables IV. and V. the results of a single year's observa- 

 tions on the larger number, measured for the first time in 1882. The trees in 

 this list only partially correspond with those used for annual observations, as a 

 considerable number of the latter, from growing too slowly or from other causes, 

 are not reliable for minute measurements. 



1, a. The Months to which the Growth of Wood is confined in Deciduous Trees. 



From the measurements made in 1880 on his five selected trees, Sir Robert 

 came to the conclusion that the growth of wood in leaf-shedding trees is con- 

 fined in general to the months of June, July, and August. I think however 

 that he underrrated the importance of the May growth. It amounted to 12 per- 

 cent, of the annual total, which it must be admitted is a substantial sum. It 

 was due however almost entirely to the three Hungary oaks, the increase in 

 the two beeches having been scarcely appreciable. Unfortunately the measure- 

 ments for 1881 were not taken till the end of June, so they are not available 

 for this inquiry. But after the unusually mild winter of 1882 the May growth 



