392 Dr Christison on the [sess. liii. 



of the same size in the same park, besides a mueli younger 

 one in the Botanic Garden, and younger limes in both 

 situations. 



Among the evergreens, a Sequoia girjantca and an African 

 cedar in the Botanic Garden, and an Austrian pine at Craigie- 

 hall, averaged about 1| inch, the two first being a little 

 below and the last a little above it ; an AMcs Lowiana and 

 a Cedrus Dcodara, 1 inch, all being between 2 and 3 feet in 

 girth. A Douglas pine in the Botanic Garden averaged 1^ 

 for forty-five years, before failing, just as the decennial obser- 

 vations began. The rate of a Cuprcssus Lawsoniana, 18 

 inches in girth, at Craigiehall, was -f of an inch ; of an 

 Araucaria there and another in the Botanic Garden, neither 

 of them fine specimens, about § of an inch ; and that of the 

 largest yew, 6 feet in girth, nearly h an inch. 



2. Annual Hate of Increase in Height in different Species 

 of Trees. 



The rate of upward growth is much more difficult of 

 measurement than the rate of girth-increase. In deciduous 

 trees of any size it is impossible by the direct means of 

 measuring rods, and if a rough estimate of height may 

 l)e obtained l)y the hypsometer, the dil'ticulty of fixing the 

 position of the true top, on which accuracy with this instru- 

 ment depends, is so insurmountable, that it is vain to 

 attempt annual observations in this way. In the case of 

 young deciduous trees, although tlie difficulties are less, 

 they are sufficient to make experiments troublesome and 

 unreliable. 



With evergreens, and particularly pines, it is different. 

 Their erect and well-defined top-shoot shows the top un- 

 erringly ; yet even in tlicm it is surprising how difficult it is 

 to attain accuracy witli measuring rods, except in quite 

 young trees not nuich above the heiglit of a man. 



Probably for these reasons Sir llobert Christison made no 

 attempt to measure the U])waT'd gTowth from year to year ; 

 but in 1879 he tcjok the height of a Hungary oak and of 

 a consideral)l(i iniml)er of cvei'green trees l)y means of rods, 

 and in 1887 I retook them by the same method, with the 

 aid of my brothers. The total amount for nine years is thus 

 known, and a fair margin for inaccuracy ol)tained in striking 



