NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. I47 



The outer margin of 1944 at 11.8 cm. is rather weak and poorly 

 developed locally; at 2.8 cm. the entire outer margin is weak and 

 irregular. 



Since the lens is exterior, it ceases at some point between 11.8 

 and 2.8 cm. Analysis gives three diameter flushes for two tip flushes 

 for two years. Some radii, of course, show three sharp contacts for 

 two years. 



TTP 20-30 has two diameter flushes for two tip flushes for two 

 years and is very nearly the ultimate in simplicity. However, the 

 1943 increment has several thin arcs of slightly narrower cells buried 

 in compression wood in the lightwood zone. This is taken to represent 

 one of the earliest evidences of growth rhythm as mentioned under 

 TTP 20-27 above. 



Table 7S.—TTP 20-31 



{Right branch') 

 6.5 cm. 2.7 cm. 0.8 cm. TF 



1943-1944 I see I see i see 3 



(Left branch) 



7.7 cm. 1.8 cm. TF 



1943 I see I 



1944 I see I see i 



The sections of TTP 20-31 (table 78) contain a rather curious 

 situation in the two branchlets which arose from the outer end of 

 1942 tip growth. From the right branch, sections were taken at 6.5 

 cm. from the middle of the first tip flush of 1943 ; at 2.7 cm. from the 

 middle of the second tip flush of 1943; and at 0.8 cm. from the 

 middle of 1944 tip growth. No section contains more than one 

 growth layer except for sections at 2.7 cm. which show short arcs of 

 interrupted densewood four to six cells in from the cambium. From 

 the left branch, sections were taken at 7.1 cm. from the middle of the 

 single flush of 1943, and at 1.8 cm. from the middle of 1944 tip 

 growth. Each diameter flush accompanied one tip flush. Such dis- 

 crepancy between two branchlets which arose from almost exactly 

 the same point, one a terminal and the other a large lateral bud, is 

 difficult to explain, (i) It is possible, but not probable, that the 

 original blocks from which sections were cut became mixed. The 

 slides were compared with the blocks and agreed satisfactorily. (2) 

 The right branch is abnormal in the sense that elongation occurred 

 without corresponding diameter increase. However, the diameter of 



