202 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



of 1943 tip growth and its absence in sections h, it would seem that a 

 large share of 1943 tip growth consisted of primary xylem and bark 

 only. If a section could be taken some years later at the position oi b 

 sections, it would be lacking one annual increment. A longitudinal 

 section showing the geometrical design of annual additions of tip 

 growth is commonly oversimplified in view of the two contrasting 

 types of terminal xylem described above. 



A stage somewhat intermediate between TTP 20-3-c and TTP 

 22-1, and TTJ 4-3, is given in TTJ 4-4 which was cut off on July 27, 

 1944, after having been measured on the same dates as TTJ 4-3. In 

 1943, TTJ 4-4 put on 12.7 cm. tip growth and in 1944, 8.8 cm. The 

 ratio of these figures is in marked contrast to that of diameter growth. 

 Sections a, taken 3 cm. above the base of 1943 tip growth, showed i 

 msce for 1943 and i see plus i inc for 1944. The growth layer for 

 1943 averaged one-fourth the thickness of 1944 growth in spite of the 

 fact that 1943 tip growth was nearly 50 percent greater. In sections h, 

 taken 3 cm. inward from the outer end of 1943, the i msce for 1943 

 was still half as wide as in a. A gradual conical tapering apparently 

 does not characterize the branch ; the outer termination of the xylem 

 must be rather abrupt. In sections b, farther out, the outer border of 

 the see of sections a has become indefinite. 



TTJ 4-5 duplicates TTJ 4-3 by possessing primary xylem only in 

 the outer part of 1943 tip growth. 



Measurements of tip growth were made on TTJ 5-3, on March 14, 

 1942, January 9, 1943, February 5, 1944, and July 28, 1944, and gave 

 13.8 cm. for 1942, 15.9 cm. for 1943, and 13.6 cm. for 1944 up to 

 July 28, 1944, when the sections were cut. Sections a, taken 4 cm. in- 

 ward from the outer end of 1941 tip growth, show strands of primary 

 xylem for 1941, i see for 1942, i msce for 1943, and i dee plus i inc 

 for 1944. Sections b, taken 3 cm. outward from the inner end of 1942, 

 contain a thin growth layer for 1942, i msce for 1943, and i dee plus 

 inc for 1944. Sections c, taken 2 cm. inward from the outer end of 

 1942, contain strands of primary xylem for 1942, i msce for 1943, and 

 I dee plus I inc for 1944. Sections d, taken 3 cm. outward from the 

 base of 1943, contain for 1943 and 1944 the same as did sections c. 

 Sections e came from 1944 tip growth and contain i inc. 



Thus, secondary xylem may fall markedly short of the outer end of 

 the tip flush, or it may reach out into the terminal bud. 



Lateral buds and dual tip flushes. — This pertains to the relation be- 

 tween lateral buds and dual tip flushes in those cases where the lateral 

 buds arise from, and are a portion of, the terminal bud. Those buds 



