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



271 



alternation of thick and thin, sharply bordered growth layers (text 

 fig- 47) : 



1. I average gl with frost injury dinner 1938 



2. I very thin gl = "outer thin" gl of 1938 



3. I average gl = inner 1939 



4. I very thin gl = "outer thin" gl of 1939 



5. I average gl = inner 1940 



6. 2 very thin gls = outer 1940 



7. I average gl = 1941 



XSC 1 2- 1 -a, cut October 11, 1941, gives even a better signature (text 

 fig. 46 ; pi. 32) : 



1. I average gl 



2. 2 thin gls 



3. I very thin gl 



4. I average gl 



5. I thin gl 



6. I average gl 



7. 2 thin gls 



8. I average gl 



= inner 1938 



= outer 1938 



= outermost 1938 



= inner 1939 



= outer 1939, an "outer thin" 



= inner 1940 



= outer 1940 



= 1941 



Fig. 47. — XSC 12-2-a. Increments for 1938-1941. Variability of thickness and 

 multiplicity giving a pattern similar to what has been called a "fingerprint." 

 I average gl == ist 1938; i very thin gl = 2d 1938; i average gl=:ist 1939; 

 I very thin gl = 2d 1939 ; i average gl = ist 1940 ; 2 very thin gls = outer 1940 ; 

 I average gl = 1941. Without criteria of absolute dating the pattern could be 

 ascribed to growth for 8 years. 



All the "outer thin" growth layers have the same general ap- 

 pearance, no matter in which specimens they exist. But it must be 

 borne in mind that trees XSC and TTC were under observation and 

 were dated accurately. 



