Ill] 



THE EFFECT OF TEMPERATURE 



119 



of easy determination, and it is a point of considerable interest 

 to compare the phenomenon in evergreen and in deciduous trees. 

 I happen to have no measurements at hand with which to make 

 this comparison in the case of our native trees, but from a paper 

 by Mr Charles E. Hall* I have compiled certain mean values for 

 growth in the climate of Uruguay. 



19 20 



years 



Fig. 30. Half-yearly increments of growth, in cadets of various ages. 

 (From Daffner's data.) 



Mean monthly increase in Girth of Evergreen a?id Deciduous Trees, 

 at San Jorge, Uruguay. {After C. E. Hall.) Values expressed 

 as 'percentages of total annual increase. 



Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 



Evergreens 9-1 8-8 8-6 8-9 7-7 5-4 4-3 6-0 9-1 11 -1 10-8 10-2 

 Deciduous 



trees ... 20-3 14-6 90 2-3 0-8 0-3 0-7 1-3 3-5 9-9 16-7 21-0 



The measurements taken were those of the girth of the tree, 

 in mm., at three feet from the ground. The evergreens included 

 species of Pinus, Eucalyptus and iVcacia ; the deciduous trees 

 included Quercus, Populus, Robinia and Meha. I have merely 

 taken mean values for these two groups, and expressed the 

 monthly values as percentages of the mean annual increase. The 

 result (as shewn by Fig. 31) is very much what we might have 

 expected. Th^ growth of the deciduous trees is completely 

 arrested in winter-time, and the arrest is all but complete over 



* Trans. Botan. Soc. Edinburgh, xvm, 1891, p. 456. 



