170 



Relation of Annual Rings to Age. 



observable that, in many cases, the growth of the stem is not 

 uniform upon all sides ; or, in othe"r words, a cross-section would 

 show axes of unequal length and an elliptical section. In such 

 cases, the major axis will be found in general to have the same 

 compass bearings in all trees within a certain area where they 

 are similarly influenced, thus indicating a common and prevailing 

 force ns operating upon them. This inequality of growth, as 

 determined by my own observations, is often very considerable, 

 in twelve cases ramnn"; from 0.1 cm. to 0.95 cm. in stems 

 not exceeding 9.5 c m. in their greatest diameter, thus making 

 the maximum inequality equal to y 1 ^ of the diameter itself. A 

 very good case of this kind has been cited by Mr. T. S. Gold,* as 

 occurring under his immediate observation. This irregularity of 

 growth is well known to be due, as S:ichs has shown. j to the 

 action of the wind, which, swaying the tree back and forth, 

 causes an alternating release of tension in the tissue of opposite 

 sides of the stem. This release of tension necessarily tends to 

 accelerated growth in the subjacent tissues, and thus unequal 

 growth results, the major axis of which will coincide with the 

 direction of the prevailing winds. Assuming the longitudina 

 growth of the axis to bear the same relation to meteorological 

 conditions as the growth in diameter, the following comparison 

 for twelve years' growth of Fraxinus americana will be of 

 interest : — 



RELATION OF GROWTH IN LENGTH TO METEOROLOGY. 



Years. 



1 



1883 



1882 



1881 



3.90 



3.50 

 5.30 



1880 



3.00 



1879 



1878 



3.00 

 1.50 



1877 



1.90 



1876 



2 25 



1875 



2.35 



1874 



3.25 



1873 



1.95 



1872 



4.15 



11.50 



5.70 

 7. 25 

 4.18 

 5.40 

 3.50 

 3.35 

 7.85 

 G.95 

 7.70 

 13.10 

 8.80 



G.40 



4.15 



5 35 



4.45 



6.35 



3 00 



4.00 



7.35 



9.05 



14 70 



13.30 



11.10 



13.10 

 7 15 

 7.50 

 5.70 

 4.10 

 2.30 

 2.10 

 4.10 

 6.90 

 11.20 

 12.50 

 7.35 



2.50 

 2.60 

 3.00 

 2.35 

 2.60 

 1.75 

 2.30 

 3.75 

 3.70 

 3.90 

 3.15 

 4.20 



3.70 

 3.70 

 4.60 

 3.10 

 2.55 

 2.00 

 1.90 

 2.90 

 4.00 

 4.60 

 3.20 

 3.00 



9.60 



6.00 



9.90 



9.35 



11.50 



4.60 



4.00 



10.10 



1 9.30 



16.50 



27.50 



25.40 



* Pop. Science Monthly, Vol. X, p. 379. 

 f Text Book of Botany, p. 813. 



