22 



CLIMATIC CYCLES AND TREE GROWTH 



distribution, non-symmetrical on the + and — sides (above and below the 

 mean). Complacent ring records show a symmetrical distribution with far 

 too many values near the mean (see fig. 10b) ; sensitive records show a skew 

 distribution with increased numbers away from the mean (see fig. 10c). 



Fig. 10 — a. "Normal" distribution of data about mean. 



PPT( Pikes Peak timber line) 

 .Complacent (b) 



PP B ( Pikes Peak Basin) 

 Sensitive (c) 



> -_ 



1.8 



2.0 



Fig. 10 — b, c. Frequency distributions compared : standardized rings widths 

 in complacent and sensitive records, 1750-1920. 



At various times attempts have been made to plot curves in different ways 

 referred to above to see if any advantage became obvious. But none ap- 

 peared and it has always been felt that the simplest possible presentation of 

 the data was the most advisable. 



The skeleton plot (fig. 11) was used as early as 1921, but came into extensive 

 use in 1927 for the cross-dating of rings. It simply represents in proper time 

 order the notably undersized rings in any series. In Arizona similarities 



