1886-87.] Dr Christison on the Girth of Trees. 51 



On the Monthly Increase in Crirth of Trees at the Royal 

 Botanic Garden, a,ncl at Craigiehall, near Edinburgh. 

 By David Chkistison, M.D. 



(Read 14tli April 1887.) 



In a paper read to the Eoyal Society of Edinburgh in 

 March 1883 I gave the results of monthly girth-measure- 

 ments of eleven trees, taken by Sir Eobert Christison in the 

 three previous years, and of the same trees, with thirty-five 

 others, taken by myself in 1882. As stated at the time, 

 these observations were too limited to allow of perfectly 

 reliable deductions being made from them ; but as they have 

 since been continued for five* additional years, considerable 

 confidence may now be placed in the accuracy of the results. 

 In considering them, however, I shall only make use of the 

 last four years' observations in the case of deciduous trees, 

 and of the last five years' observations in the case of ever- 

 greens, as it was only in these years that the growth for the 

 month of April was ascertained. 



The principal subjects which I shall endeavour to elucidate 

 from my observations are, — the beginning and the end of the 

 growing season, and the proportional growth . of different 

 species in each month of the growing season. 



I. Commencement of the Growing Season in Deciduous 

 Trees. 



Sir Eobert Christison concluded, from three years' experi- 

 ments on five deciduous trees, that substantial increase in 

 girth in that class of trees began in June, but evidently full 

 confidence could not be placed m general deductions derived 

 from observations on so small a number of trees. Accord- 

 ingly, to test the question further, I experimented in 1882 

 upon twenty-eight trees, and found that not less than 16 

 per cent, of their annual increment took place before the 

 month of June. Five years' subsequent observations have 

 fully confirmed this result. 



Having ascertained, by the observations of 1882, that a 



* For four years only, when this paper was read ; but the observations for 

 1887 having since been concluded, I have been able to take advantage of this 

 additional year, thereby increasing the number of years from which the averages 

 are struck. 



