l6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



Growth-layer characteristics. — Table 4 shows the average of year- 

 to-year variations of growth-layer thicknesses on single tree sequences 

 and on three groups. These figures are the measured equivalents of 

 the visual values embodied in the terms variable, fairly variable, and 

 uniform. In the main, the numerical results militate against judgment 

 by eye. Tree HPC 5, for instance, was judged variable and HPC 6 

 uniform ; yet both have nearly the same average variation. However, 

 greater consistency is shown by groupings : for the period, 1 898-1 941, 

 the average of the variable sequences is 0.36, of the fairly variable 

 0.32, and of the uniform 0.28. 



Table 4 emphasizes the importance of location, not species, as the 

 apparent determinant of average variation. For instance, trees HPC 

 3 and 6 are both foxtail pines and yet have variations of 0.37 and 



Table 4. — Holnian Pass collection 

 Average year-to-year variation 

 1898 1850 1898 



to to to to 



1897 1941 Entire 1897 1941 



HPC 1 1850- 0.22 0.40 0.30 G 10 0.26 0.40 



2 1850- 0.35 0.41 0.38 II 0.38 0.27 



3 1850- 0.31 0.43 0.37 7 0.21 0.27 



4 1880- 0.36 0.28 0.30 



5 1850- 0.29 0.19 0.25 



6 1850- 0.27 0.21 0.24 



7 1850- 0.18 0.35 0.26 



9 1857- 0.40 0.39 0.40 



0.24, respectively (0.43 and 0.21 for 1898-1941), the higher value 

 existing in the drier location. It is true that the ponderosa pines have 

 higher variations in general than the other species but HPC 3, a fox- 

 tail pine, grew between HPC i and 2 and has even a slightly higher 

 average variation. 



All trees from the wetter locations (group 11) had higher average 

 variations for the period 1850- 1897 than they did for the period 

 1898-1941. In contrast, the trees in the drier locations (group 10) 

 had lower average variations in the earlier period. 



Tables 5 and 6 giving average growth-layer thicknesses and average 

 departures were prepared even though definitive results were not 

 expected because secular trend and long-period fluctuations had not 

 been eliminated. In table 5, group 10 shows an increase and group 11 

 a decrease of average growth-layer thicknesses from the period 1850- 



