194 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



that the branch responded only a very sHght degree to the forces 

 causing a growth slowdown ; nonetheless, the tendency is there. 



Cross sections made through 1944 tip growth of WCh 2-1 contain 

 I see. In sections a, one-third of the way out in the flush, short arcs 

 are present but it can only be assumed that they might correspond to 

 tip growth slowdown. 



The second type of tip growth — early setting of terminal bud — 

 was not measured on tree WCh 2. However, an example, WCh 3-1, 

 is well shown on text figure 43. Here tip growth began immediately 

 after April 26, attained 6 cm. by April 30, began to slow down May 

 28, and ceased by June 14 (June 3 for WCh 3-2). The growth slow- 

 down of branches which were to set early terminal buds occurred at 

 exactly the same time as it did on those branches which were to grow 

 continuously until September. By July 23 the whole tree, WCh 3, was 

 resting, all terminal buds set. 



It is of interest to note that sections a of WCh 3-1, 12 cm. out from 

 base of 1944 tip flush and 36 cm. from tip of branch, contain i see 

 plus one long diffuse arc whereas the wide-field binocular shows two 

 growth layers on unstained sections. Sections b, 9 cm. from tip, con- 

 tain I see plus one fairly indefinite growth layer which shows as one 

 growth layer under a wide-field binocular. 



Tip-growth type consisting of two flushes separated by terminal bud 

 scale scars cannot be shown graphically because weekly measurements 

 did not include such a branch. Those trees and branches not measured 

 were observed constantly, sometimes daily. In general, it is true that 

 times of rapid tip growth coincided on different branches and on dif- 

 ferent trees and with discrete flushes on branches which set intra- 

 seasonal terminal buds, and that plateaus of growth slowdown (WCh 

 2-1) coincided with intervals of no growth on branches with multiple 

 tip flushes in one season. Such correspondence holds true, even to the 

 extent that when the third interval of rapid tip growth began on WCh 

 2-1 a few terminal buds on other branches and other trees expanded 

 sufficiently to separate the bud scales, but grew no farther. 



The growth for 1944 in WAp 1-3 comprised two tip flushes of 36.5 

 cm. and 4 cm. Sections a, 3.5 cm. in from the outer end of 1943 tip 

 growth, contain i see for 1943 and i dee plus i see for 1944. Sec- 

 tions b, 18.2 cm. out from the base of 1944, contain i dee and i see, the 

 dee interpreted as belonging to the first tip flush and the see to the 

 second. Sections c, 9 cm. inward from the outer end of first flush, con- 

 tain 2 dee and i see. The outer dee, two-thirds and more out in the 

 diameter growth of 1944, no doubt corresponds to the first flush of 

 1944. Sections d, 0.5 cm. outward in second 1944, contain a narrow 



