NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 1 69 



and was cut off May lo, 1940. In the 1938 increment, complexity and 

 sharpness increase inward on the branch. 



XSC 8-1 (table no) was frozen artificially at 41 cm. on May 9, 

 1941, and was cut off immediately. The so-named "growth layer" of 



1938 at 52 cm. was caused by the natural frost of April. It seems prob- 

 able that one of the lenses of 1940 at 52 cm. became an entire growth 

 layer at 41 cm. In this connection, attention should be called again to 

 longitudinal variations; for instance, the uniformity of 1938 in XSC 

 3-2 and of 1939 in XSC 8-1, and the variation outward, especially of 



1939 in XSC 6-1 and of 1940 in XSC 8-1. 



Table hi. — XSC 8-3 



1938 



1939 



1940 



1941 inc inc inc 



XSC 8-3 (table in) was frozen artificially May 9, 1941, at 46.5 

 cm., and was cut off May 11, 1941. One of the arcs of 1938 at 61 cm. 

 was frost-made. The sharp lens of 1940 becomes concurrent at 33 

 cm. Outward on the branch from 61 cm. to 46.5 cm. and 33 cm., the 

 differences in ring patterns and sequences are noteworthy. This branch 

 should be compared with XSC 8-4. 



XSC 8-4 (table 112) was frozen artificially May 9, 1941, at 50 cm., 

 and was cut off May 13, 1941. The longitudinal uniformity of this 

 branch should be contrasted with the variation along branch XSC 8-3. 



XSC 9-2 (table 113) was frozen artificially at 43 cm. May 9, 1941, 

 and was cut off May 30, 1941. The growth of 1941 is up to seven- 

 eighths as thick as that of 1940; the outer half-dozen cells are im- 

 mature, and of these the outermost are very narrow. Plates 26, 27, 

 and 28, fig. I, show one form of longitudinal variation in tree XSC 9. 



