84 Sir Robert Christison oii the 



difference in radial growth thus indicates an inferiority of 

 26 per cent, during the hitter year compared with the 

 former. This exceeds the loss of other pines, hut the larch 

 is not evergreen.] 



It appears then tliat evergreen trees suffered rather less 

 than trees with deciduous leaves. A sufficient cause will be 

 pointed to presently. But in the first place let me turn 

 attention to a singular difference of the like kind among 

 Ifeaf-shedding trees themselves. I liave placed together at 

 the end of that list rill the oak tribe, including the hornbeam, 

 which is closely allied to the true oaks. This has been 

 done to show their agreement in the property of resisting 

 the influence of an unfavourable season, injurious to Other 

 triees with deciduous leaves. Of eight observations one may 

 be excluded, as made on a Craigiehall oak which in 1878 

 inust have been subjected to some special cause of inferior 

 growth. The other observations were made on three healthy 

 common oaks {Q. pechmculata), and one each of Turkey oak 

 {Q. Cerris), Hungary oak (Q. Fannonica), American red oak 

 (Q. rubra), and hornbeam (Carpinus Behdus). I regret that 

 [ had only one tree of the four last species at my command. 

 But, using such opportunities as I possessed, it appears that 

 the Slim of these seven measurements, all very close to 

 one Another for the two years, is an increase of 5-70 inches 

 for 1878j and 5-15 for 1879, — being a difference of a tenth 

 only, or 10 per cent. 



If we now separate the oak tribe from the other leaf- 

 shedding trees, it will be found that the aggregate growth 

 of trunk in the latter was for 1878 8-6 inches, and for 1879 

 5*05 inches, — being a reduction actually of 41 per cent., or 

 between one-third and one-half. The eft'ect of a bad-gro wing- 

 season is thils made very conspicuous on a considerable 

 variety of species of our most common and familiar forest 

 trees. 



The cause, or rather the causes, of this inferiority of 

 growth, are not far to seek. It may be said that, as there 

 was generally in 1879 no material defect in foliage on which 

 the growth of wood depends, there was no sufficient reason 

 against its usual annual increase. But there was one positive 

 cause against it, and two others extremely probable. 



In the first place, the usual five months of growing 



