NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 1 75 



wood, thin zones of slightly narrower cells form a rhythmic pattern. 

 In 1939 of XSC 1 1-3, in contrast with XSC lo, the outer growth 

 layer is thicker and cannot he called an "outer thin" growth layer. The 

 densewood of this outer growth layer becomes threadlike outward at 

 44 cm. The densewood band of the partly sharp, complete, entire 

 growth layer at 38 cm. is replaced outward at 29 cm. by three bands 



of diffuse densewood. In 1940 the sharp lenses are compound. The 

 mostly sharp lens is a concurrent system of two lenses, one of which 

 is sharp and the other diffuse-margined. On the whole, the two 

 branches of XSC 11 possess a relatively high degree of continuity 

 along their lengths. 



XSC 12-1 (table 122) was frozen artificially at 42 cm. on May 9, 

 1941, and was cut off October 11, 1941. In the 1938 increment, the 

 three sharp, complete, entire growth layers at 48 cm. are weaker than 



