26 



CLIMATIC CYCLES AND TREE-GROWTH. 



only. A comparison between the 5 and these oldest 2 taken by them- 

 selves give an agreement not absolutely perfect, yet so close that 

 errors thus introduced will not materially affect the curves. However, 

 the oldest 2 were very slow-growing trees and they required on the 

 average an increase of about 30 per cent in order to make their curve 

 continuous with the whole 5. Thus the tree-record is made to begin 

 at 1385. In the recent years of the record also, between 1891 and 1896, 

 a slight correction was made for omitted rings, the complete omission 

 of a ring being an exaggeration that introduces error. 



Year 



1870 



1880 



1890 



1900 



1910 



25 sections measured in 1904-6 



h 



Summer 

 May 1 to Nov. 1 



1900 



1910 



Year 



1900 



1910 



Year 



FIG. 4. Comparison of two Flagstaff groups. Variations in annual rainfall 

 according to month of beginning annual means. 



