NO. I GROWTH LAYERS IN TREE BRANCHES — CLOCK ET AL. 203 



which are coordinate with, and those which arise at the base of, the 

 terminal bud are not here included. 



It had become quite clear by 1942 that the number of tip flushes on 

 the pines was not consistently the same for all branches for any one 

 year; some branches grew one tip flush whereas others grew two. 

 Late in 1942 it was noted that branches with two tip flushes for a cer- 

 tain year had had a lateral bud attached to the terminal bud above its 

 base at the close of the previous season. Doak (1935) had recorded 

 such a possible relationship in 1935 ; Stone and Stone (1943) were to 

 note it in 1943. If it should prove to be true that the presence of a 

 lateral bud above the base of the terminal bud predetermines two tip 

 flushes the following season, then such tip flushes are controlled by 

 circumstances in existence during the season prior to the one in which 

 the actual multiple growth occurs. 



Our evidence is neither exhaustive nor conclusive. Different cases 

 may be summarized : 



1. Lateral buds on terminal — 2 tip flushes next season. 



2. No lateral buds on terminal — 2 tip flushes next season. 



3. Lateral buds on terminal — i tip flush next season. 



4. No lateral buds on terminal — i tip flush next season. 



On January 30, 1943, TTP 20-33 had a lateral bud 2.3 cm. above the 

 base of the 2.5-cm. terminal bud. On February 5, 1944, the branch 

 showed tip growth in two flushes, the inner of 6.8 cm. and the outer 

 2.2 cm. The branch TTP 20-34 bore two lateral buds 1.3 cm. above the 

 base of the 2.4-cm. terminal bud in January 1943. Tip growth for 1943 

 included two flushes, one of 3.0 and the other of 1.6 cm. TTP 20-40 

 also illustrates case ( i ) but with this difference : the first tip flush 

 measured 1.4 cm. and the second 13.3 cm. At the start of the season, 

 the 2.8-cm. terminal bud bore a lateral bud 2.3 cm. above its base. If 

 this lateral bud did have genetic significance for future tip flushes, 

 then its position longitudinally on the terminal bud had no significance 

 as regards the relative lengths of the two subsequent tip flushes. TTP 

 23-9 carried two lateral buds 1.3 cm. above the base of the 2.3-cm. 

 terminal bud prior to the 1943 season. At the end of that season, tip 

 growth showed an inner flush of 4.2 cm. and an outer flush of 1.2 cm. 

 The two lateral buds which were on the terminal bud had expanded 

 into two branches, thus apparently establishing a direct genetic con- 

 nection between the lateral buds and the subsequent dual tip flushes. 

 Yet this is just one example. 



Examples under case (2) are as numerous as those under case (i) 

 among the branches devoted to special study. In TTP 20-16, tip 

 growth for 1942 comprised an inner flush of 7.3 cm. and an outer one 



