22 CLIMATIC CYCLES AND TREE-GROWTH 



wall or with very slight bracing, so that at a glance one may look over 

 the entire collection. 



The original surface of the stump is placed downward in the mount- 

 ing, thus showing the freshly cut surfaces, which at a little distance 

 below the stump-top are in better condition. One or both of these 

 surfaces is smoothed with a rasp or file; then after careful inspection 

 of the rings a line or band is marked where the measuring and dating 

 will be done. For this purpose two parallel lines a half inch or more 

 apart are put on, as nearly straight as possible. The space between 

 these lines is then shaved with a sharp razor. This leaves a superb 

 surface for measuring the rings. The lighting direction is important, 

 but by a little practice the best position is readily found. The only 

 special caution at this stage is that each break in the wood which 

 has been glued should be marked and shaved along the crack so that 

 dating and measuring can be carried past it without the slightest 

 chance of error, but this rarely presents any difficulty. 



RADIAL STUDIES 



CIRCUIT UNIFORMITY 



By circuit uniformity is meant the close similarity of the ring 

 records in all directions from the center of the tree. The funda- 

 mental importance of this was fully recognized in the first formative 

 period of this investigation. Cross-identification between different 

 trees was first used as an essential in 1911, but this identity between 

 different radii in the same tree was noticed in the very first trees 

 measured in 1904. To describe where it has been found would be to 

 enumerate almost every tree worked upon. Even groups that do not 

 cross-identify well show circuit uniformity. This does not mean that 

 the different radii are equal, but that the relative ring values are 

 closely the same in all directions. So the present topic is for the pur- 

 pose of calling attention to a few exceptions. Circuit uniformity 

 is modified in three ways — by eccentricity, lobes, and gross-rings. 



Eccentricity — Slight eccentricity is very common. It becomes 

 noticeable in perhaps one-third of the stumps examined and occurs in 

 perhaps one-quarter to one-twentieth of the trees sampled. It merely 

 means more growth on some one side than on the opposite. It is a 

 common effect of group pressure and frequently occurs when two 

 trees grow very close together. The maximum growth is then away 

 from each other. It may be due to other causes. In the first 25 

 Flagstaff yellow pines there was 12 per cent more growth to the north- 

 east than in the opposite quadrant, attributed to better moisture con- 

 servation in the shade of the tree. Eccentricity, unless excessive, need 

 have no effect whatever on the tree record, and even if excessive it can 

 usually be evaded. The most extraordinary case ever noted was a 



