400 



Dr Christison on the 



[sEss. Liir. 



To estimate the indirect or prolonged loss caused by the 

 three severe seasons is naturally unattainable with any pre- 

 cision. Perhaps it is fairly represented at the very least by 

 the difference between the amount in the year before the 

 disastrous seasons and the highest amount reached after 

 them. This, as we have already shown, would represent a 

 loss to the deciduous class of 22 per cent., and to the ever- 

 greens of 15 per cent. Against this we have to set off the 

 loss which might have been sustained, even in ordinary 

 seasons, from natural diminvition of growth in trees past 

 their prime, but which in so short a period would probably 

 not have been great, and the possibility of the girth-increase 

 rallying in some trees even after nine years of depression, 

 which I am inclined to think is quite possible. 



3. Incidence of the Loss in the three consecutive Severe 

 Sea-sons. — The depression of the girth-increase during the 

 three trying seasons did not go on augmenting from year to 

 year, as might have been expected. On the contrary, in the 

 deciduous class, as a whole, there was a great rally in the 

 third year, and in the evergreens there was at least no great 

 additional loss in that year. Taking the trees individually, 

 not a single case of progressive decrease throughout the 

 three years occurred among the reliable deciduous trees, 

 while there were eight such cases among the evergi-eens. In 

 further illustration of this fact, I have ascertained that in the 

 deciduous class the maximum loss occurred in 23 out of 26 

 trees, and in 13 out of 15 species in 1880, and in only 2 

 trees in 1881 ; wliile in the evergreens it occurred in only 

 5 out of 24 trees in 1880, and in 11 trees in 1881. Also 

 that, if we take the trees in the Botanic Garden only, 19 in 

 number of each class, the following are the variations in 

 incidence that occurred : — 



Not atlcL-tc'd ill 1870, 

 Foil olJin 1879, . 

 Fell off ill 1880, . 

 Irnprovfd in 1880, 

 Fdloirin 1881, . 

 Iixiproved in 1881, 



