NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. I29 



tion that each sharply bordered growth layer must necessarily be an 

 annual increment, we have the interesting but impossible situation of 

 nine annual increments for five years. 



Much the same information is yielded by TTC 36-7-b (text figs. 

 25, 26) which includes four years, 1939-194^. A general analysis 

 gives : 



Table si.— TTC 36-7-h 



1939 — I sce+ddw 



1940 — 2 see 



1941 — I sce+i sL+i d iL 



1942 — I sce+i psce+2 s arcs+i d arc 



Here, four years include six sharp growth layers. Some radii show 

 seven sharp contacts and one radius gives the maximum of eight 

 sharp contacts under low-low power. 



Four radii have been selected on TTC 33-6-a (text fig, 5). The 

 differences between radii 2 and 3, and i and 3, are especially note- 

 worthy. In fact, the sequence of sharp contacts is different on each 

 radius and one can readily see the difficulties inherent in correlating 

 from one radius to another if the surface of the section between two 

 radii is unavailable. As a matter of passing interest, tip growth of 

 branch TTC 33-6 was measured February 21, 1942, January 9, 1943, 

 January 22, 1944, and July 31, 1944, when the branch was cut off. 

 Sections a were cut from the 1942 tip growth. Because this branch 

 was growing when cut, at least one more growth layer would have 

 been formed before the general close of the growing season. 



The growth of one year is equally effective as an illustration of 

 radial variation. Text figure 30 of TTC 33-1 i-a, shows the growth 

 increment of 1940 on two opposite radii. Without the rest of the sec- 

 tion, correlation would be neither simple nor certain. The interior of 

 the increment actually contains two simple arcs and one compound 

 arc. It is the central arc which is compound and diffuse at one ex- 

 tremity and sharp bordered at the other. Over more than half the 

 circuit the outer densewood zone is divided into three bands, else- 

 where into two, the entire zone being referred to as multiple dense- 

 wood. 



Text figure 37, TTC 33-13-a, shows the increment for 1942 

 wherein a radius can be so chosen as to contain i, 2, 3, 4, or 5 sharp 

 contacts. 



Although text figure 13, XSC i-i-b, does not contain the entire 

 cross section, enough of 1939 appears to show that the 1939 annual 



