408 ])r Christison on the [sess. liii. 



are perhaps extreme cases ; but taking quite ordinary ex- 

 amples, we have the beech No. 14, with an increase of 0"60 

 in 1882 and 0-40 in the next year ; the oak No. 16, with 0'95 

 in 1885 and 0"50 in 1887 ; and even among the steadiest of 

 the evergreens we have Sequoia No. 1, with 1-75 in 1882 and 

 1*05 in the next year. Perhaps five years may be sufficient 

 to establish a fair average, if any very unfavourable year be 

 rejected. 



7. The depressing effect upon girth-increase of disease or 

 injury may be prolonged for years after the date of the dis- 

 ease or injury, even when the affected trees appear perfectly 

 healthy. It has been shown that the effects of the hard 

 winters of 1879, 1880, and 1881 were prolonged in not a few 

 of the trees till 1887. But special diseases or injuries may 

 produce the same effect. Thus the horse chestnut No. 9 

 increased three-quarters of an inch in 1881, but the foliage 

 was destroyed apparently by early frost in 1882, the growth 

 almost entirely ceased that year, and during the next five 

 years, although the foliage was always healthy and remark- 

 ably luxuriant, the increase averaged only the 5th of an 

 inch. 



8. A question of much interest is whether trees which 

 have suffered a prolonged depression in their girth-increase, 

 from low winter temperatures or other causes, will eventually 

 recover their normal rate. A longer period of observation 

 must elapse before this question can be settled in the case 

 of most of the affected trees. Undoubtedly in the decennial 

 period under review, the majority of such trees have shown 

 no tendency to improve, and some have gone on from bad to 

 worse, but in a few instances a decided and probal)ly lasting 

 rally has taken place, as in Firms excelsa No. 2G, wliicli, after 

 six years at the low average of 0'34, has improved in the 

 last four years to 0G8 ; and in Cedrus Dcoclara No. 29, which, 

 after five years at the average of 0'58, has risen in the 

 last four years to 112. The two evergreen oaks also rallied 

 in a marked degree in 188G from their long seven years' 

 depression, each of them having increased half an inch, and 

 although a new wave of depression swept over them in com- 

 mon witli otlier evergreens in 1887, and reduced their increase 

 to a quarter of an inch, the reduction may prove to be only 

 temporary. 



