NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. I9I 



1941 and 1942. Sections a, from the inner needle zone of 1941, 18 

 cm. from base of terminal bud, contain i see for 1941 and i see plus 

 patches of psg for 1942; sections h, from the outer needle zone of 

 1941, 1 1.5 cm. from base of terminal bud, contain i see plus one sharp 

 arc for 1941 and i see plus psg for 1942; sections c, from the inner 

 needle zone of 1942, 7.5 cm. from base of terminal bud, contain i see 

 plus psg ; and sections d, from the outer needle zone of 1942, 0.8 cm. 

 from base of terminal bud, contain i see. Multiple diameter flushes to 

 match multiple tip flushes, as marked by sets of bare-needle zones, 

 exist for 1942 inward from 18 cm. on the branch. Outward from 18 

 cm. the evidence for multiple diameter growth, although more limited 

 than inward, is present in 1942 and also in 1941. 



TTP 24-10 comprised the inner and TTP 24-22 the outer part of a 

 branch cut January i, 1943. The inner set of bare-needle zones of 



1942 tip growth measured 5 cm. and the outer set 1.6 cm. with a ter- 

 minal bud of 1.5 cm. On May 16, 1942, when artificial freezing was 

 applied, only the inner set of bare-needle zones was present. It is 

 possible that recovery from the impact of frost stimulated a second 

 tip flush. Terminal bud scale scars were absent between the two sets 

 of bare-needle zones. The sections show i see for the two sets of 

 bare-needle zones except for an extra growth layer in the immediate 

 vicinity of 40 cm. inward from base of terminal bud. 



The presence of multiple sets of bare-needle zones does not neces- 

 sarily determine multiplicity in diameter growth. Among the series 

 from which the above illustrations have been taken, there are a few 

 branches bearing only one set of bare-needle zones. TTP 24-14, cut 

 January i, 1943, did not possess dual sets of bare-needle zones. Sec- 

 tions a, 55 cm. from tip of terminal bud, in 1937 tip flush, contain i 

 see plus one sharp lens for 1941 and i see plus ddw for 1942. Sec- 

 tions h, 43 cm. from tip, in 1938 tip flush, contain i see for 1941 and 

 I see plus one sharp lens plus ddw plus psg for 1942. Sections c, 32 

 cm. from tip, in 1939 tip flush, contain i see for 1941 and i see plus 

 ddw for 1942. Thus, in TTP 24-14, single sets of bare-needle zones 

 (and one tip flush) accompany multiplicity in diameter growth. 



TTP 24-16 and 24-17 possessed single sets of bare-needle zones and 

 single growth layers for each year of 1941 and 1942. 



In summary of the bare-needle zone problem it may be said: (i) 

 In the outer part of a branch (say 18 to 20 cm. from base of terminal 

 bud), multiple sets of bare-needle zones seldom are recorded in visible 

 diameter multiplicity. This rather closely parallels the situation 

 where the multiple tip flushes are separated by terminal bud scale 

 sears. (2) Inward on branches, however, there is a much greater 



