NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. I95 



see which, in thickness, corresponds to the growth layer outward from 

 the dee in the other sections. WAp 1-3 gives a case of two diameter 

 flushes (or growth layers) for two tip flushes in one year. 



During 1944, WCh 2-3 formed two tip flushes, the first of 66 cm. 

 and the second of 4 cm. Growth in WCh 2-3 ceased between Septem- 

 ber 3 and 10. In contrast, many second flushes on other branches of 

 the same tree had ceased growth on or shortly before August 6. This 

 early date corresponds to the second plateau of WCh 2-1, text figure 

 43, whereas the later date corresponds to the summit plateau. Sec- 

 tions a of WCh 2-3, taken 12 cm. out from the base of the first 1944 

 flush, contain i see. Sections b, 7.5 cm. inward from the outer end of 

 first 1944, contain i msec plus i see. The msce is almost wholly 

 sharp around the circuit. Why did not the intra-annual msce of sec- 

 tions b appear in sections a, 46.5 cm. inward on the branch? Did the 

 added diameter growth corresponding to the second tip flush cease 

 inward between b and a, or did the growth slowdown (or cessation) 

 become less inward until, at a, diameter growth was, insofar as visi- 

 bility is concerned, continuous? Evidence exists for the occurrence 

 of both cases of longitudinal variation in other branches and other 

 trees. Sections c, i cm. outward from the base of second 1944, con- 

 tain I see. 



Branch WCh 2-6 was observed in regular course during 1944 and 

 especially so in 1945. Tip growth for 1944 contained two flushes, the 

 first "very long" and the second 2.8 cm. ; for 1945 tip growth was 26 

 cm. in one flush. Sections a, ly cm. inward from the outer end of first 

 1944, contain 2 dee plus i see for 1944 and i see for 1945. One dee 

 is one-third of the way out in 1944 diameter growth whereas the 

 other, which probably corresponds to the second tip flush, is seven- 

 eighths of the way out. Sections b, taken just outward from the base 

 of second 1944, contain i see for 1944 and i dee (frost induced) plus 

 I see for 1945. In sections a, the unstained materials under a wide- 

 field binocular appear to have three growth layers; in sections b, 

 probably one growth layer. Both of these wide-field binocular ap- 

 pearances are erroneous. A summary of sections a gives 2 see plus 2 

 dee for 3 tfs in 2 years; sections b, 2 see plus i dee for 2 tfs in i>< 

 years. 



The above examples will perhaps suffice to illustrate the three dis- 

 tinct types of tip growth found among the angiosperms observed, as 

 well as the variations in the relationships of tip growth to diameter 

 growth in any one type. There is, however, a transitional form de- 

 serving of mention, the decreased distance between what seemed to be 

 undeveloped leaves. Many of the branches in the top of WCh 2 



