NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. l6$ 



A preliminary study of lightwood, densewood bands, and compres- 

 sion-wood zones reveals many detailed alternations of rows of narrow 

 and wide cells. It appears highly reasonable that these inconspicious 

 alternations, together with the more gross forms of growth layers, 

 record a marked sensitivity to fluctuating physiological conditions. 

 This refers not to random irregularity but to an alignment of cells in 

 a tangential direction. 



Table 103. — XSC 1-5 Table 104. — XSC 2-1 



g2 cm. 53 cm. 66 cm. 51 cm. 



1936 I see 2 see I934-I93S •••• 7 see 7 see 



I msce 2 sL 2 sL 



I dee 2 ddw 2 ddw 



^ 1936 I see I see 



1937 I see I see 7 sL 7 sL 



I sL 



2 ddw 



1937 3 see 3 see 



2 sL 2 sL 



^938 ^ ^^'^^ 1938 I see I see 



2 sL. 



I msL 1939 I see i see 



I s iL 2 sL 2 sL 



I msL 

 1939 I msce I see 



I sL 1940 inc inc 



ddw 



1940 I see 



4 sL 

 I psL 

 I dL 



The branch XSC 2-1 (table 104) was frozen artificially on 

 April 8, 1940, and cut from the tree May 10, 1940. At 66 cm. the 

 two lenses of 1939 are so thin that they might be called widely divided 

 densewood. They expand outward, at 51 cm., into a distinct lens sys- 

 tem, which means the lenses thin inward but lose no definition. The 

 mostly sharp lens at 51 cm. is overlapping. 



XSC 2-1 gives us a case where the growth layers are equally sharp 

 along the branch and, except for 1939, show striking vertical uni- 

 formity. 



Branch XSC 2-2 (table 105) was frozen artificially at 79 cm. on 

 April II, 1940, and was cut from the tree May 26, 1940. The dense- 

 wood of the outer lens of 1934 at 67 cm. extends completely around 

 the circuit. In 1936 at 67 cm., the outer margins of the sharp, com- 

 plete, entire growth layers are not as sharp as they are inward on the 



