Mar, 1892.] THE BOTANICAL SOCIETY OF EDINBURGH. 279 



No. 20 is in the south belt and No. 89 in the north belt 

 of the Arboretum. Both throve well till 1891, when they 

 were thickly sprinkled with small bluish- white spots, looked 

 sickly, and had their girth-increase considerably lowered. 

 No. 20 seems to have been the quicker grower of the two, 

 its rate being 1*22, while that of No. 89 is only 0-94, but 

 this may be because the latter was measured higher up. In 

 their best years No. 20 attained 1"75 and No. 89, 1'15. 



B. Collective Kesults. 



(1) Deciduous Trees. 



a. Comparative Annual Rate of the S^jecies. 



In considering this question I have taken only the 

 quickest grower of each species, because two or three 

 specimens are not sufficient to establish a fair average of 

 growing power when one or two of them are in comparatively 

 poor soil, or have shown signs of unhealthiness, as happened 

 with several of my selected trees. It must also be remem- 

 bered that even if the trees were in equally favourable 

 conditions of soil, situation, and healtli, their rates might 

 not be strictly comparable, because, although all young, they 

 are not actually of the same age ; and even if they were, a 

 further source of error arises from the different periods of 

 life at which the species may be in the habit of passing from 

 the slow rate of infancy to the rapid rate of youth. There- 

 fore the figures in the first column of Table I. must be accepted 

 not so much as comparative of the growing power of the 

 difit'erent species as indicative of their rate in tolerably good 

 soil, or in poor soil, as the case may be. 



[Table I. 



