1888-89.] Annihol Increase in Girth of Trees. 399 



spring than the deciduous class, and therefore may have 

 suffered more from earlier exposure to the prolonged cold of 

 that season. The fact, however, that the deciduous girth- 

 increase rallied materially in the third severe season, when 

 the winter temperatures were lower than in the other two, 

 proves that excessively low winter temperatures may not 

 be sufhcient in themselves to produce disastrous results, 

 and that other circumstances are required to conduce to 

 that end, such as deficient ripening of wood in autumn, the 

 period in winter when the low temperatures occur, warm 

 sunshine quickly following frost, protection or the reverse 

 by snow, sudden thawing, and unfavourable weather in 

 spring. 



2. Loss ofThiiber 'produced ly these Severe Seasons. — This was 

 both direct and indirect ; that is to say, loss in the unfavourable 

 years themselves, and loss from the prolongation of their 

 effects to subsequent years. In estimating the first, the 

 most natural mode might seem to be by comparison of the 

 increase in these years with the average increase for the 

 decennial period. But by this method not only the depress- 

 ing effect of the seasons at the time, but their prolonged 

 effects on girth- increase would be ignored. A fairer com- 

 parison may be made with the year 1878, which preceded 

 the disastrous seasons. It is true this season may have been 

 imusually favourable, but I do not think it was remarkably 

 so, as not a few of the trees, which escaped lasting injury^ 

 grew more rapidly in some of the years after the severe 

 seasons, than in 1878, the year before them. By this com- 

 parison a loss comes out in the deciduous species, as dis- 

 tinguished from trees, of 30, 46, and 22 per cent., and in the 

 evergreens of 22, 15, and 25 per cent., in 1879, 1880, and 

 1881 respectively. 



It would be rash to assume, however, that this loss repre- 

 sents the loss sustained by trees in full vigour in the Edin- 

 burgh district, because a number of the selected trees, judg- 

 ing from the slowness of their growth, were no longer in 

 their full vigour in 1878 ; and it is yemarkable that almost 

 without exception it was in such trees that the greatest loss 

 was sustained. Still, even as applicable to trees past their 

 prime, a permanent or serious temporary check to growth 

 represents a very heavy loss. 



TRANS. BO?. SOC. VOL. XVII. 2 E 



