64 SIR ROBERT CHRISTISON AND DR CHRISTISON ON THE 



average, fell at Edinburgh : then the evergreens made a surprising rush, no 

 less than 31 per cent, of their annual growth taking place, whereas in August 

 1880 the portion was only 9 per cent., and in 1882, 13 per cent. This result 

 was the more remarkable, as the temperature of the month was 2° "3 below the 

 average. The deciduous trees were also apparently benefited by this excessive 

 rain, although accompanied by deficient temperature, their proportion being 34 

 per cent, in August and September of 1881, while it was only 27 per cent, in 

 1880, and 25 per cent, in 1882. 



1882. — The rainfall of March, April, May and June was abundant, exceeding 

 the average by an inch in each of the first two months, and being rather above 

 the average in the third and fourth. In the same period the growth of ever- 

 green wood was large, but this may easily be accounted for by the mild winter 

 and early spring, without calling in the aid of the rainfall. 



Taking a general view of this investigation, it appears as if an abundant 

 rainfall were favourable to the growth of wood, but much more favourable to 

 the evergreen than the deciduous class. It must be admitted however that a 

 longer series of observations, taken on a larger scale, are necessary to determine 

 this point. The most striking fact shown is the extraordinary increased growth 

 of the evergreens in August 1882, along with a very heavy rainfall and low 

 temperature, whereas in the previous August, when the conditions were 

 reversed, the rainfall being 2*46 inches in default and the temperature 3 0, 3 in 

 excess, the evergreen growth was very deficient. 



Summary. 



To give a better idea of the general scope of this paper, the details of which 

 are necessarily of a somewhat dry and tedious character, I now give a summary 

 of the chief conclusions which are scattered throughout the text. It must be 

 remembered however that these conclusions are strictly applicable only in the 

 Edinburgh district, and that some of them are only indications of the probable 

 truth, and require to be confirmed by a larger series of observations. 



1. The effects upon the growth of wood of the severe winters preceding the 

 growing seasons of 1879, 1880, 1881 were not the same in deciduous and ever- 

 green trees. In 1879 both suffered : the former more than the latter. In 

 1880 a further decline took place in the deciduous class, but not in the other. 

 In 1881 the deciduous class recovered their loss of the previous year, but it was 

 now the evergreen's turn to fall off. After the unprecedentedly mild winter of 

 1882 they again differed. For while the deciduous trees made no further 

 recovery, the evergreens regained the loss sustained in 1881 ; neither class 

 however attaining to the standard of growth in the favourable season of 1878. 



2. Evergreen trees probably do not increase their wood at all in winter, 



