l8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. Ill 



The data in table 7 were calculated in an attempt to obtain a 

 measure of excess variation over normal. From the earliest to the 

 latest periods shown, HPC i, 2, 3, and 4 show a rise and decline; 

 HPC 5, 6, and 9 show a general decline ; and HPC 7 shows a general 

 rise of values. Six of the trees, but not including HPC i, have 

 lower values for 1910-1941 than for 1850-1897. As in the case of 

 average departures, it is HPC i and 7 which do not conform. In 

 spite of their influence, group 7 shows a slight but progressive 

 decline from the earliest to the latest period. If HPC i and 7 are 

 eliminated from group 7, giving group 7 (restricted), the decline 

 becomes more decided. 



Table 7. — Holman Pass collection 



Average departure from mean variation 



1850-1897 1898-1941 1910-1941 



HPC I 0.17 0.28 0.24 



2 0.21 0.24 0.20 



3 0.25 0.26 0.23 



4 0.23 0.24 0.21 



5 0.20 0.13 O.II 



6 0.19 0.16 0.15 



7 o.is 0.23 0.24 



9 0.28 0.25 0.20 



G 10 0.132 0.148 0.136 



II 0.204 0.118 0.1 10 



7 o.iio 0.105 0.094 



7 (restricted) 0.130 0.105 0.092 



Table 8 brings together a short summary of characteristics on the 

 wood in order to emphasize the differences between the two periods 

 1850-1897 and 1898-1941. Although the differences between groups 

 10 and II appear striking, they actually are due to the influence of 

 two out of eight trees. Elimination of those two trees from group 7 

 brings it into harmony with group ii. There remain, then, the 

 fundamental differences between the periods 1850- 1897 and 1898- 

 1941. Do they reflect a change in amount of rainfall with its attendant 

 changes in rainfall characteristics, or a change in the rainfall interval 

 important to tree growth, or both, or some other change? In a pre- 

 vious paragraph a striking dearth of trend agreements among the 

 trees was pointed out for 1850- 1897 in contrast with succeeding years. 

 A reexamination of the data shows that the dearth does not apply 

 quite so drastically to the trees from the wetter locations. This 



