Figure 5.

Relationship between the cross-sectional sieve element area of a vein and (A) the cross-sectional tracheid area of a vein and (B) the cross-sectional area of the entire vein for individual second-, third-, and fourth-order veins from the Swedish ecotype grown at 14°C under 400 μmol photons m⁻² s⁻¹. Individual veins (n = 52) were segregated by sieve element (SE) number and ratio of phloem area/vein area into veins containing ≤14 SEs and phloem area/vein area ≥0.5 (black squares; putative minor loading veins) or ≥15 SEs and phloem area/vein area <0.5 (open squares; second order veins). Linear regression lines drawn for each segregated group of veins (≤14 SEs or ≥15 SEs), and statistically significant differences in slope and intercept (ANCOVA) between regression lines is indicated (n.s. = not significant at P ≤ 0.05). Linear regression analyses for each line are (A) y = 0.12 x + 47, R² = 0.34, and P < 0.01 (black squares) and y = 0.14 x + 46, R² = 0.54, and P < 0.01 (open squares); (B) y = 0.03 x + 24, R² = 0.64, and P < 0.001 (black squares) and y = 0.04 x − 11, R² = 0.91, and P < 0.001 (open squares).