56 CLIMATIC CYCLES AND TREE-GROWTH. 



In nearly every decade some are thus distinguished, and in each century 

 there are usually 3 to 4 conspicuously small rings which give very 

 important aid. 



In the first work on the 2,200-year sequoia record, the identification 

 was a laborious task involving all the writer's spare time for a year. 

 The only real difficulty was with the ring for the year 1580. This was 

 temporarily called 1580A, but the material collected in 1919 showed it 

 to represent a year and a final and complete renumbering included it as 

 such. In the end the comparisons gave entire confidence as to the 

 identity of every ring. Section No. 2 gave the most nearly perfect 

 long record, beginning at 274 B. C., and is used as a standard with 

 which to compare all new ones. 



The most difficult parts to identify are the compressed rings. Over 

 long periods, varying from 5 or 10 up to 100 years, the rings are some- 

 times so crowded together that large numbers of them seem to be 

 merged into one and their identification becomes extremely difficult 

 and in a few cases impossible. The great variations in sizes so produced 

 also exaggerate effects. These groups of compressed rings are con- 

 sidered as of little value, and in fact in many trees their measurement 

 is omitted altogether. Tree No. 12 of the sequoias obtained from the 

 Indian Basin had such bad groups of compressed rings that it proved 

 practically impossible to identify them without a large expenditure of 

 time not then available. Tree No. 17, also, from Camp 7, was found so 

 full of compressed rings in the last few hundred years that all measure- 

 ments were omitted after the year 1130 A. D. 



Fire-scars. Most of the big trees show fire-scars at some time in 

 their history, and the process of the tree's regeneration is very inter- 

 esting to observe. If the scar is small the woody growth quickly 

 comes in from each side and covers it. If the scar is very large, occupy- 

 ing perhaps one-quarter or one-third of the circumference, the tree 

 is likely never to recover and the burnt place remains permanently 

 on its side. In cases of less extensive burns, the wood from each side 

 year by year grows toward and over the injured spot, and if the injury 

 has not been too great the approaching sides may meet and imprison 

 their own bark within the tree. Thus one often sees the tops of the 

 stumps marked here and there by a hole as large as a foot in diameter, 

 filled with bark in perfectly good condition. 



No. 12 had several fire-scars that interfered with the identification 

 of rings. No. 18 also had one or two fire-scars and in particular showed 

 a fire in the year 1781. The latter evidently stopped the growth at 

 that point completely, yet was not large enough to interfere with 

 recovery. In the sample in the laboratory the usual reddish-colored 

 heartwood changes about the year 1700 to the white sap wood, which 

 ends with the ring 1781 and shows a surface that was once covered with 

 bark. However, immediately outside of that surface, the red heart- 



