122 DOUGLASS— CHARACTERS IN ANNUAL RINGS. 



ground is four times the minimum in dry ground and is accompanied 

 by profound dififerences in type of ring ; the eleven-year solar period 

 (of the double-crested, dry-climate type) shows with rapidly increas- 

 ing distinctness as one passes from the complacent, moist-ground 

 trees of the basins to the very sensitive, dry-soil trees of the uplands 

 and of Arizona. The climatic feature considered in this paper is the 

 reality of certain possible climatic cycles found in the trees. That 

 these cycles are real is attested by the extent both in time and space 

 over which they are traced. This conclusion enables us to trace in 

 the rings of the sequoia a provisional outline of solar variation for 

 the last 3,000 years. 



Stew^vrd Observatory, 



University of Arizona. 



i 



