l88 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I40 



contain one incomplete, entire growth layer plus a zone of narrow 

 cells in the form of a broken circle — the merest hint of an intra-annual. 

 In sections h, from the inner needle zone, the diffuse broken growth 

 layer is a trifle more definite. Sections c and d, from the outer 

 bare and outer needle zones respectively, contain only incomplete 

 lenses for 1942. There is here, then, some evidence of a fluctuation in 

 the rate of diameter growth to correspond with a like variation in the 

 rate of tip growth. The broken thin band of narrow cells in sections a 

 occurs about five to seven cells inward from the cambium in the as yet 

 immature xylem. Of course, it might well be that a definite entire 

 band of narrow cells is not in existence because of immaturity and 

 that such a zone might have been present had the 1942 growth been 

 permitted to go to maturity. 



The sections from TTP 20-21 were cut off the tree May 7, 1942. 

 At the time of cutting, 1942 tip growth contained two sets of bare- 

 needle zones not separated from each other by terminal bud scale 

 scars. The inner set measured 9 cm. and the outer set measured 3 cm. 

 The terminal bud was 0.8 cm. long. Three pistillate cones arose from 

 the base of the outer bare zone. Sections a from the inner bare zone 

 contain i see and one incomplete, entire growth layer. The i see 

 makes up three-fourths of the total xylem, thus comparing favorably 

 with the proportions between the two sets of bare-needle zones in the 

 tip growth. Sections h from halfway out in the inner needle zone 

 contain one incomplete, entire growth layer. Farther out the branch, 

 the sections from the second set of bare-needle zones contain an incom- 

 plete lens each. Insofar as sections a are concerned, TTP 20-21 gives 

 a clear-cut example of two growth layers for two sets of bare-needle 

 zones, and there would be no hesitation in correlating the two. Sec- 

 tions b, however, do not show the extra growth layer, and its absence 

 can only mean that a growth layer to match a tip flush is present in- 

 ward on the branch but absent outward. It may well be that a tree 

 makes a special effort to keep vital processes continuous near the 

 growing tips, 



TTP 20-21 with two growth layers suggests that TTP 20-20 with 

 a hint of an extra growth layer is a transition between TTP 20-15 

 with I see and TTP 20-21 with 2 see. Apparently the presence of a 

 lateral bud between the two sets of bare-needle zones of TTP 20-15, 

 the three pistillate cones of TTP 20-21, and neither in TTP 20-20 

 gives evidence that they have no significance as markers, either of a 

 second tip flush or of a second diameter flush. 



The 1941 tip growth of TTP 24-9 contained two sets of bare-needle 



