NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. I35 



and a second, sharp over more than half the circuit. On some radii, 

 therefore, both contacts are sharp, whereas on others, one is sharp 

 and one is diffuse, the latter of course being an obvious "double," 

 The two growth layers correspond to two tip flushes. In contrast, the 

 increment for 1939, with two sharp contacts throughout, has one tip 

 flush. 



The sections of TTC i-ii (table 54) were cut November 24, 1945 ; 

 this gives nine years of record. In sections at 244 cm., the nine incre- 

 ments contain 19 sharp contacts, or, counting simply the sharp, com- 

 plete, entire growth layers and the wholly sharp lenses, they contain 

 16 sharp, complete growth layers and these represent nine years. The 

 maximum number of growth layers sharply bordered in whole or in 

 part is 29 in sections at 244 cm. Five additional are completely dif- 

 fuse and, under the microscope, would readily reveal their intra- 

 annual character. 



It is also worthy of note that the complexity of the growth-layer 

 display in general decreases outward on the branch, from 244 cm. to 

 30 cm. from the tip. 



Correlation of growth layers from section to section, as between 

 244 cm. and 212 cm., is especially difficult. Consider 1940. Which 

 intra-annual at 244 cm. corresponds to the half-lens at 212 cm.? At 

 132 cm., in 1940, all intra-annuals have disappeared, not because they 

 have been cut out longitudinally by the pith (1939 surrounds pith at 

 132 cm.) but because they actually have been terminated, leaving the 

 annual increment as one sharp, complete, entire growth layer. 



The increment for 1945 at 30 cm. contains an overlapping lens. 



Variations along a branch, such as TTC i-ii, are well shown by 

 comparing figure i of plate 5 with figure 2 of plate 5 and figure i of 

 plate 6, and these with figure 2 of plate 6 and figure i of plate 7. 



The sections of TTC 33-9 (table 55) were cut from the tree Janu- 

 ary I, 1943. In 1942, at 49.5 cm., the outermost lens of the three 

 sharp lenses is concurrent. Note that the sections at 49.5 cm. have 

 seven sharply bordered growth layers for three years, growth layers 

 which carry no distinguishing intra-annual character except that some 

 of them are partial. The increment for 1942 does not change its 

 complexity outward on the branch, but it does change its nature to a 

 considerable extent. 



The long lens of 1939 in TTC 34-1 (table 56) becomes an entire 

 growth layer outward on the branch, but it does not follow of course 

 that the lens disappears inward, or if it does, that it does not reappear 

 even farther down the branch. In 1940 the lens becomes longer out- 

 ward. Artificial freezing on May 18, 1941, killed the cambium out- 



