GROWTH OF WOOD IN DECIDUOUS AND EVERGREEN TREES. 



59 



The increase of the yews was nearly equally divided between the first and 

 second periods of the season. The former had indeed a slight advantage, but 

 the spring of 1882 was unusually early, and a longer experience may show 

 that yews do not follow the rule of early growth which appears to hold 

 good in most of the Pinacese. 



As it may be of some interest to show the comparative rate of growth of 

 wood in certain species of trees under observation, I give the following Table : — 



Table IX. — Average Increase in Girth of Eight Species of Trees for Three Years. 





1880. 



1881. 



1882. 



Average. 



Average of — 



Inch. 



Inch. 



Inch. 



Inch. 



3 Hungary oaks, 



1-20 



172 



1-75 



1-55 



1 American and 2 Turkish oaks, . 



0-45 



0-75 



0-65 



0-62 



9 Beeches, ..... 



0-53 



0-64 



0-79 



0-65 



4 Sequoias, ..... 



1-46 



117 



1-40 



1-01 



3 Araucarias, .... 



0-65 



0-51 



0-66 



0-61 



2 Deodars, 



0-42 



0-30 



0-82 



0-51 



4 Yews, ..... 



0-31 



0-37 



0-50 



0-39 



1 African cedar, .... 



1-75 



1-40 



1-60 



1-58 



III. Influence of Weather on the Growth of Wood. 



This is a complicated inquiry, so many and various are the influences which 

 may come into play. Extreme frost, prolonged frost, the amount of heat and 

 sunshine, drought or excessive rain, strong winds, all no doubt affect the 

 growth of wood, their influence varying with the seasons, and not necessarily 

 showing their effects immediately. 



Of all these agents cold is probably the most energetic ; I have there- 

 fore looked to it mainly for explanation of the differences in annual growth, 

 adopting Mr Sadler's record of temperature in the Botanic Garden as my 

 guide, because the greater number of the measured trees are situated either 

 there or in the adjoining Arboretum. The thermometers used by him are four 

 feet from the ground, and being unprotected the readings are not strictly 

 accurate, but for purposes of comparison with each other the observations are 

 sufficient. 



Sir Robert Christison showed that the remarkable cold and absence of 

 sunshine in the spring and summer of 1879 caused a great deficiency in the 

 growth of wood, both in deciduous and evergreen trees, in that year as com- 

 pared with the previous one ; that the deficiency was greatest in the deciduous 

 class ; and least of all, so far as his observations went, in oaks. 



In 1880 the spring was favourable to the opening buds, the temperature 



