Figures (9)  Tables (1)

    • Figure 1. 

      Flowchart showing the progression of the investigation and examples of stem anatomy at the beginning and end. The stem segment at lower left shows stem diameters below the apical whorl of buds, and the segment at lower right shows diameters at the base of the leader.

    • Figure 2. 

      Overview cross sections of stem segments at an apical position approximately 1 cm below the hormone application site. The text at upper right in each photomicrograph indicates the treatment. (a) Black arrow points to evidence for the first periderm enveloping the cortex; the white arrow points to an enlarged cortical resin duct; numerous small ones are also evident. (b) Labels indicate cortex, phloem (Ph) and secondary xylem (xylem) locations. (c) Thinner section than those shown in Fig. 2a & b but otherwise similar. (d) Parenchyma have proliferated and preexisting resin ducts are enlarged or stretched radially. (e) Note the diffuse porosity throughout the cortex and the band of large diameter resin ducts immediately centrifugal to the phloem. (f) Radial enlargement of preexisting resin ducts and proliferation of cortical parenchyma, but lacking is an external band of new resin ducts just beyond the phloem. (g) Preexisting resin ducts are radially enlarged (arrow). (h) Circumferential band of resin ducts has developed external to the phloem. (i) A similar response to that shown in Fig. 2e.

    • Figure 3. 

      Cross sectional anatomy of the cortex surrounding secondary xylem (staining blue green) at approximately 1 cm below the apical ends of stem segments. (a) Lanolin control, showing cortical resin ducts (d), mature phloem (ph) and secondary xylem (x). The arrow indicates dormant vascular cambium. (b) ACC treatment, showing evidence for browning (arrow) of secondary cell walls in the cortex and phloem. (c) IAA treatment, radially elongated ducts (white arrow) and greatly enlarged parenchyma (black arrow). (d) IBA treatment, numerous enlarged parenchyma (white arrows); ducts retained their circular appearance.

    • Figure 4. 

      Higher magnification images of cortical tissue. (a) Early stage of cortical duct formation near the outer phloem interface; the wall of a plasmolysing cell is arrowed. (b) Primary wall (arrowed) fully collapsed. (c) Tonoplast (arrowed) of an expanded vacuole in a greatly enlarged cell. (d) Walls of several collapsed cells in the vicinity of a partially collapsed are arrowed; note wall thickness and the staining reaction possibly indicative of lignin or suberin. (e) An early duct (d) surrounded by two tiers of sheath cells with collapsed and collapsing cells (arrowed) nearby. (f) Active production of cells (one arrowed) to produce the inner sheath tier surrounding a duct (d). (g) A duct (d) surrounded by three tiers of sheath cells having contents probably indicative of resin production.

    • Figure 5. 

      Woody duct formation as observed in cross sections (a)−(e) and (i), and radial longitudinal sections (f)−(h) of balsam fir cortex. (a) Early stage of a developing woody duct (d) encased by variable number of parenchyma tiers (arrow) and most of the duct opening filled with intrusive parenchyma. (b) A slightly more advanced stage with the former duct opening completely filled with parenchyma, some differentiating woody elements, and nascent cambium (c) developing on its outer periphery. The arrow indicates a ray-like string of enlarged parenchyma cells bisecting the woody element population. (c) A more advanced stage of cambium (c) formation in a developing woody duct. (d) The cambium (c) in this woody duct is fully developed but the woody elements appear to be at different stages of secondary wall formation (arrow). (e) A fully mature woody duct bisected by a radial file of parenchyma cells (p). (f) An intrusive tip (arrow) of a parenchyma cell elongating within a cortical duct. (g) Low magnification, showing a longitudinal strand (arrow) containing woody elements and non-woody parenchyma and running axially through the cortex. (h) A longitudinal section through a cortical woody duct showing its cambium (c) with elongated nuclei (black arrow) and internalized parenchyma (p). The duct's woody elements all appear to have annular ribs of the primary xylem type (white arrow). (i) This low magnification cross section through the circular attachment pad of a mature leaf shows the spatial association of the leaf base to a woody duct (arrow).

    • Figure 6. 

      Developmental responses, as seen in cross sections, of stem segments the apical ends of which were treated with lanolin (only), IAA in lanolin, IBA in lanolin, and a combination of IAA and IBA in lanolin. In each of the four columns of photomicrographs, the apical end is shown at the top, followed by the mid-stem region, and the basal end at the bottom. Lanolin column: (a) Non-dividing CZ, several phloem cells per radial file; (b) non-dividing CZ; (c) same as Fig. 6a but with 2−3 RE cells and, as shown in the inset, in scattered locations around the circumference a single TE per radial file. IAA column: (d) new TEs; (e) a single RE and a single thin-walled TE per radial file; (f) RE cells without TEs. IBA column: (g) new TEs; (h) RE only; (i) no RE or TE cells. IAA + IBA column: (j) new TEs; (k) RE cells only; (l) RE cells only.

    • Figure 7. 

      Examples of xylogenic responses, as viewed in cross sections, of stem segments the apical ends of which were treated with a combination of IAA + ACC in lanolin, IBA + ACC in lanolin, and IAA + IBA + ACC in lanolin. In each of the three columns of photomicrographs, the apical end is shown at the top, followed by the mid-stem region, and the basal end at the bottom. IAA + ACC column: (a) Several new TEs per radial file; (b) 1−2 TEs; (c) 1−2 RE cells only per radial file. IBA + ACC column: (d) several new TEs; (e) 1−2 RE cells and no TEs; (f) a single RE cell, 1−2 new TEs and a very narrow CZ. IAA + IBA + ACC column: (g) a single RE cell and no new TEs; (h) a narrow CZ and a single TE; (i) several new TE cells per radial file.

    • Figure 8. 

      Sections of balsam-fir cambium and xylem that display variable darkening of intercellular spaces. (a) Brightfield radial section of cambial zone (cz) bordering latewood (LW) and stained with toluidine blue. The white arrow indicates a darkened compound middle lamella region and the black arrow an absence of similar darkening. (b) The white arrows indicate intercellular spaces between procumbent xylem ray cells that stained less intensively to toluidine blue. (c) SEM of a xylem ray in radial section; the arrows point to intercellar spaces between the procumbent ray cells. (d) Tangential section showing two rays on the centripetal periphery of the cambial zone. The arrow points to an intercellular space between the radial wall of a fusiform cell and that of a ray cell. (e) Tangential section of a 2-celled ray in the cambial zone, the small arrow pointing to evidence for an intercellular space between fusiform and ray cell walls. An axially oriented 'spear tip' (large arrow) appears to contain particulate matter and to be intruding between what had been adjoining walls of two fusiform cells. (f) Radial section (interference contrast optics) of phloem (Ph), cambial zone (CZ), radially expanding cambial derivative (RE) and differentiating TEs in proximity to latewood (LW). The arrows point to accumulations of insoluble matter within or paralleling the axial walls.

    • Figure 9. 

      Hand-cut sections of untreated balsam-fir dormant stems: (a), (c) and (e) are unstained sections; (b), (d), (f) and (g) are stained with toluidine blue. (a) Radial section of dormant cortex showing the abscission zone (a) and axially oriented leaf trace (t) of the mature first-year leaf (l), also showing a resin duct (d), latewood (LW) and vascular cambium (c). (b) Cross section basal to the leaf abscission zone (a) of the leader showing the cortical leaf trace (t); the inset at higher magnification shows the trace as a woody duct. (c) An unstained cross section at midway along the length of a 3-year-old balsam fir needle, showing its central vascular strand (s). (d) Tangential section of a 3-year-old balsam fir needle base at its stem attachment point showing the singular leaf trace (t) entering the stem. (e) Radial section of a 3-year-old balsam fir stem showing the vascular strand in the leaf (s) passing through the abscission zone (a) into the woody duct leaf trace (t) in the periderm. The trace traverses the cambium (c) and runs radially through three annual layers of secondary xylem (arrow) to the pith (p). (f) Cross section through the trace-cambium junction of a 3-year-old balsam fir stem, with vascular cambium (c) and latewood (LW) also indicated. Note that most leaf-trace cells are radially elongated but thin walled. (g) Cross section through latewood (LW) of the second year and earlywood (EW) of the third year in a 3-year-old balsam fir stem showing the size and anatomy of the leaf trace. (h) Cross section through second year earlywood in a 3-year-old balsam fir stem; the trace comprises mostly tracheids but also has living cells (arrow) that appear to be sieve elements.

    • Treatment Mean number of cells per radial file
      Apical end Midstem Basal end
      lanolin
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 3 4 1 0 8 4 4 1 0 9 5 5 1 0 11
      2 4 5 1 1 11 5 4 1 0 10 4 6 1 2 13
      3 4 6 0 0 10 3 5 1 0 9 3 4 2 0 9
      4 2 4 0 0 6 4 6 0 0 10 3 4 1 0 8
      Mean 3.3 4.8 0.5 0.3 8.8 4.0 4.8 0.8 0.0 9.5 3.8 4.8 1.3 0.5 10.3
      Std. Dev. 1.0 1.0 0.6 0.5 2.2 0.8 1.0 0.5 0.0 0.6 1.0 1.0 0.5 1.0 2.2
      ACC
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 4 4 2 0 10 2 6 0 0 8 4 6 1 2 13
      2 3 4 2 0 9 3 5 0 0 8 3 5 2 1 11
      3 4 4 1 1 10 4 4 1 0 9 3 4 2 0 9
      4 3 5 0 0 8 5 5 1 0 11 4 4 2 0 10
      Mean 3.5 4.3 1.3 0.3 9.3 3.5 5.0 0.5 0.0 9.0 3.5 4.8 1.8 0.8 10.8
      Std. Dev. 0.6 0.5 1.0 0.5 1.0 1.3 0.8 0.6 0.0 1.4 0.6 1.0 0.5 1.0 1.7
      P: ACC vs lanolin 0.337 0.201 0.119 0.500 0.350 0.271 0.353 0.269 1.000 0.274 0.337 0.500 0.104 0.365 0.367
      IAA
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 5 6 5 3 19 5 4 1 2 12 3 4 2 1 10
      2 4 4 1 3 12 2 2 2 0 6 3 0 4 0 7
      3 2 6 3 2 13 3 6 1 1 11 4 6 3 0 13
      4 2 4 2 3 11 3 4 1 2 10 2 2 4 0 8
      Mean 3.3 5.0 2.8 2.8 13.8 3.3 4.0 1.3 1.3 9.8 3.0 3.0 3.3 0.3 9.5
      Std. Dev. 1.5 1.2 1.7 0.5 3.6 1.3 1.6 0.5 1.0 2.6 0.8 2.6 1.0 0.5 2.6
      P: IAA vs lanolin 0.500 0.375 0.036 0.000 0.032 0.181 0.233 0.104 0.040 0.432 0.140 0.138 0.008 0.338 0.340
      P: IAA vs ACC 0.386 0.149 0.095 0.000 0.042 0.395 0.165 0.049 0.040 0.319 0.180 0.138 0.022 0.201 0.231
      IBA
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 4 8 4 2 18 6 4 2 0 12 3 6 0 0 9
      2 5 6 2 1 14 5 2 2 1 10 3 2 2 0 7
      3 2 4 1 2 9 2 2 3 0 7 2 2 2 0 6
      4 2 4 1 1 8 2 6 2 0 10 2 2 2 0 6
      Mean 3.3 5.5 2.0 1.5 12.3 3.8 3.5 2.3 0.3 9.8 2.5 3.0 1.5 0.0 7.0
      Std. Dev. 1.5 1.9 1.4 0.6 4.6 2.1 1.9 0.5 0.5 2.1 0.6 2.0 1.0 0.0 1.4
      P: IBA vs lanolin 0.500 0.259 0.061 0.009 0.120 0.416 0.151 0.003 0.196 0.414 0.038 0.092 0.338 0.196 0.028
      P: IBA vs ACC 0.386 0.143 0.209 0.009 0.144 0.423 0.111 0.002 0.196 0.287 0.025 0.092 0.338 0.108 0.008
      P:IBA vs IAA 0.500 0.337 0.262 0.009 0.314 0.348 0.353 0.015 0.065 0.500 0.180 0.500 0.022 0.196 0.081
      IAA + ACC
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 3 7 3 1 14 2 5 3 0 10 3 7 3 2 15
      2 4 8 2 1 15 3 6 2 2 13 3 8 3 1 15
      3 3 3 4 2 12 2 4 2 0 8 2 6 1 3 12
      4 2 6 2 3 13 1 4 2 2 9 2 5 0 0 7
      Mean 3.0 6.0 2.8 1.8 13.5 2.0 4.8 2.3 1.0 10.0 2.5 6.5 1.8 1.5 12.3
      Std. Dev. 0.8 2.2 1.0 1.0 1.3 0.8 1.0 0.5 1.2 2.2 0.6 1.3 1.5 1.3 3.8
      P: IAA + ACC vs lanolin 0.353 0.174 0.005 0.022 0.007 0.007 0.500 0.003 0.091 0.341 0.038 0.038 0.282 0.135 0.202
      P: IAA + ACC vs ACC 0.180 0.102 0.034 0.022 0.001 0.053 0.353 0.002 0.091 0.236 0.025 0.038 0.500 0.195 0.254
      P: IAA + ACC vs IAA 0.391 0.227 0.500 0.065 0.451 0.077 0.233 0.015 0.375 0.444 0.180 0.033 0.076 0.074 0.141
      P: IAA + ACC vs IBA 0.391 0.371 0.209 0.337 0.318 0.096 0.151 0.500 0.149 0.436 0.500 0.016 0.396 0.051 0.031
      IBA + ACC
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 5 6 1 5 17 3 5 1 0 9 5 4 1 2 12
      2 6 4 2 2 14 3 4 1 2 10 5 4 2 1 12
      3 3 3 1 2 9 3 4 1 2 10 2 2 1 2 7
      4 6 8 3 5 22 4 6 1 0 11 4 2 3 0 9
      Mean 5.0 5.3 1.8 3.5 15.5 3.3 4.8 1.0 1.0 10.0 4.0 3.0 1.8 1.3 10.0
      Std. Dev. 1.4 2.2 1.0 1.7 5.4 0.5 1.0 0.0 1.2 0.8 1.4 1.2 1.0 1.0 2.4
      P: IBA + ACC vs lanolin 0.046 0.350 0.038 0.014 0.042 0.089 0.500 0.196 0.091 0.180 0.390 0.030 0.201 0.160 0.442
      P: IBA + ACC vs ACC 0.061 0.219 0.244 0.014 0.052 0.368 0.353 0.091 0.091 0.139 0.274 0.030 0.500 0.244 0.318
      P: IBA + ACC vs IAA 0.070 0.425 0.178 0.229 0.307 0.500 0.233 0.196 0.375 0.433 0.139 0.500 0.034 0.065 0.395
      P: IBA + ACC vs IBA 0.070 0.435 0.390 0.050 0.200 0.333 0.151 0.008 0.149 0.416 0.061 0.500 0.365 0.040 0.045
      P: IBA + ACC vs IAA + ACC 0.030 0.323 0.095 0.071 0.261 0.024 0.500 0.008 0.500 0.500 0.061 0.003 0.500 0.384 0.181
      IAA + IBA
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 2 2 4 2 10 4 4 1 0 9 5 6 4 0 15
      2 2 2 2 2 8 3 6 1 2 12 1 4 4 0 9
      3 2 2 2 2 8 3 8 1 3 15 3 8 1 3 15
      4 3 2 2 1 8 2 5 3 2 12 2 6 1 1 10
      Mean 2.3 2.0 2.5 1.8 8.5 3.0 5.8 1.5 1.8 12.0 2.8 6.0 2.5 1.0 12.3
      Std. Dev. 0.5 0.0 1.0 0.5 1.0 0.8 1.7 1.0 1.3 2.4 1.7 1.6 1.7 1.4 3.2
      P: IAA + IBA vs lanolin 0.065 0.005 0.010 0.003 0.423 0.067 0.178 0.122 0.034 0.066 0.178 0.123 0.124 0.293 0.174
      P: IAA + IBA vs ACC 0.009 0.001 0.061 0.003 0.160 0.271 0.235 0.073 0.034 0.045 0.228 0.123 0.229 0.390 0.225
      P: IAA + IBA vs IAA 0.140 0.007 0.405 0.015 0.028 0.376 0.095 0.338 0.276 0.129 0.402 0.053 0.242 0.189 0.118
      P: IAA + IBA vs IBA 0.140 0.018 0.293 0.269 0.102 0.268 0.065 0.122 0.046 0.105 0.398 0.030 0.183 0.126 0.019
      P: IAA + IBA vs IAA + ACC 0.089 0.017 0.365 0.500 0.001 0.067 0.178 0.122 0.207 0.134 0.398 0.324 0.269 0.310 0.500
      P: IAA + IBA vs IBA + ACC 0.012 0.030 0.160 0.067 0.040 0.312 0.178 0.196 0.207 0.101 0.152 0.014 0.242 0.390 0.155
      IAA + IBA + ACC
      Replicate Ph CZ RE SL Total Ph CZ RE SL Total Ph CZ RE SL Total
      1 2 5 2 0 9 5 6 1 1 13 3 6 1 5 15
      2 5 8 1 3 17 4 2 2 0 8 4 4 1 2 11
      3 3 6 3 0 12 5 3 3 0 11 4 8 1 3 16
      4 4 2 2 3 11 3 4 3 0 10 4 2 2 1 9
      Mean 3.5 5.3 2.0 1.5 12.3 4.3 3.8 2.3 0.3 10.5 3.8 5.0 1.3 2.8 12.8
      Std. Dev. 1.3 2.5 0.8 1.7 3.4 1.0 1.7 1.0 0.5 2.1 0.5 2.6 0.5 1.7 3.3
      P:IAA + IBA + ACC vs lanolin 0.384 0.364 0.014 0.124 0.072 0.353 0.178 0.022 0.196 0.207 0.500 0.433 0.500 0.037 0.131
      P: IAA + IBA + ACC vs ACC 0.500 0.243 0.140 0.124 0.088 0.195 0.126 0.013 0.196 0.142 0.269 0.433 0.104 0.050 0.168
      P: IAA + IBA + ACC vs IAA 0.405 0.432 0.235 0.124 0.283 0.128 0.420 0.065 0.065 0.336 0.089 0.158 0.008 0.028 0.089
      P: IAA + IBA + ACC vs IBA 0.405 0.440 0.500 0.500 0.500 0.341 0.426 0.500 0.500 0.313 0.009 0.135 0.338 0.024 0.016
      P: IAA + IBA + ACC vs IAA + ACC 0.271 0.333 0.140 0.406 0.266 0.006 0.178 0.500 0.149 0.375 0.009 0.176 0.282 0.145 0.424
      P: IAA + IBA + ACC vs IBA + ACC 0.084 0.500 0.353 0.077 0.179 0.065 0.178 0.040 0.149 0.339 0.378 0.114 0.201 0.095 0.117
      P: IAA + IBA + ACC vs IAA + IBA 0.074 0.040 0.235 0.399 0.056 0.048 0.074 0.160 0.046 0.194 0.166 0.271 0.124 0.084 0.418
      Legend (t tests): values in green, p ≤ 0.05; values in yellow, p = 0.05−0.10; values without any color, p > 0.10.

      Table 1. 

      Microscopy data and P values (95% confidence) summarized for the eight treatments.