[Campbell Biology P.835] Figure 36.3 shows the emerging phyllotaxy of Norway spruce. Given t... | Practice Question

Figure 36.3 shows the emerging phyllotaxy of Norway spruce. Given that leaf 1 is the youngest primordium, and leaves emerge in a spiral pattern, between which two developing leaf primordia would the next even younger primordium likely emerge to continue this pattern?

  • A: Between leaf 29 and leaf 42.
  • B: Between leaf 1 and leaf 6.
  • C: Between leaf 18 and leaf 23.
  • D: Directly on top of leaf 1, forming a stack.

Explanation

Phyllotaxy involves new primordia emerging in the largest available space at the shoot apical meristem, maintaining a specific divergence angle often 137.5° as mentioned in the text from the previously formed primordium. Given that leaf 1 is the youngest, the next even younger primordium would typically emerge in the central region of the meristem, between leaf 1 and one of its closest, slightly older Fibonacci neighbors, such as leaf 6 which is 5 steps older than leaf 1 in one of the spirals or leaf 9. Among the given options, 'between leaf 1 and leaf 6' is the most consistent with the general pattern of phyllotaxis in such diagrams, where the next primordium would fill the available space in the spiral.