NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 1 57 



growth layer for 1939 apparently consists of restricted lenses and, if 

 soil moisture is considered to be the dominant growth factor in the 

 extreme lower forest border, such a growth layer would indicate a 

 very dry growing season. With high magnification, however, the 

 growth layer for 1939 is seen to be entire and would indicate re- 

 stricted moisture. The cambium had limited activity but was not dor- 

 mant over much of the circumference of the section throughout an 

 entire growing season. Other branches of the same tree show normal 

 development for 1939. Such variations in one annual increment may, 

 and do, occur from tree to tree in the same general area, as was men- 

 tioned in connection with tree TTP 23. Care must be exercised, ap- 

 parently, before general ecologic or climatic conclusions are drawn. 



The increment of 1940 in TTP 24-3 has a sharp outer contact 

 except where followed by an interior lens of 1941. Over a very short 

 arc at 42 cm., 1940 is reduced to two or three rows of densewood 

 cells lying against the densewood of 1939 which, in turn, lies against 

 the densewood of 1938. 



The increment of 1941 is atypical because of artificial freezing. It 

 consists of interior and exterior concurrent lenses. Natural frost 

 injury in the interior lenses apparently dates them. Here again, it is 

 the lightwood that is lenticular — the growth layer is entire. The outer 

 growth layer consists of lenticular lightwood whose completion was 

 prevented by artificial freezing. Outward on the branch the incom- 

 plete lens becomes thin and faint. 



Table 93. — TTP 24-4 

 4Q cm. 47 cm. 41.5 cm. 2g cm. 



1937 I see 



1938 I see I see i see i see 



1939 I see I see i see i see 



1940 I see I see i see i see 



I psee 



2 dee 

 I dee 



1941 I see 



I sL 



TTP 24-4 (table 93), in contrast with 24-1, 2, and 3, has compara- 

 tively thick growth layers. What is labeled "1937" in TTP 24-4 is 

 probably second 1937. Buried within the densewood of 1938, at 49 cm., 

 there is a faint discontinuous band of narrow cells — interrupted dense- 

 wood. At 29 cm. the 1938 growth layer contains circles of compres- 



