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Question

Difficulty: HardExplicit Detail Retrieval

In her 1918 monograph on floral anatomy, botanist Agnes Arber reexamined the structural homologies of monocotyledonous leaves, challenging the prevailing view championed by Augustin Pyramus de Candolle. De Candolle had posited that the linear, parallel-veined leaves of monocotyledons represent modified petioles (leaf stalks) that expanded in the absence of a true blade—a concept termed the phyllode theory. Arber’s microscopic analyses of vascular bundle arrangement in Sagittaria species revealed, however, that while the distal leaf apex in certain taxa indeed derives from petiolar tissue, the basal sheathing regions develop from distinct foliar primordia that exhibit inversions in xylem-phloem orientation typical of true laminas. Consequently, Arber argued that monocotyledonous foliage is neither a simple petiole nor a reduced true leaf, but rather a composite structure in which petiolar and laminar developmental programs are heterochronically integrated. Crucially, Arber noted that this structural hybridity occurs exclusively in aquatic or amphibious monocot lineages, whereas terrestrial taxa retain unmodified petiolar sheaths.

According to the passage, Arber's investigation of Sagittaria species indicated that the basal sheathing regions of monocotyledonous leaves differ from the distal leaf apex in that the basal regions:

  1. develop from distinct foliar primordia exhibiting xylem-phloem inversions characteristic of true laminas.Answer
  2. B
    consist entirely of petiolar tissue that expanded in the absence of a true leaf blade.
  3. C
    are present exclusively in terrestrial monocot lineages rather than aquatic taxa.
  4. D
    lack any vascular bundle structural inversions during their development.
  5. E
    were identified by Augustin Pyramus de Candolle as representing a composite laminar structure.

Answer

The basal sheathing regions develop from distinct foliar primordia exhibiting xylem-phloem inversions characteristic of true laminas.
The passage explicitly states that Arber's microscopic analyses of Sagittaria revealed that the basal sheathing regions develop from distinct foliar primordia that exhibit inversions in xylem-phloem orientation typical of true laminas, whereas the distal leaf apex derives from petiolar tissue. The correct option directly paraphrases this explicit fact.

Step-by-Step Solution

1
Locate the specific passage section discussing Arber's findings on Sagittaria species and basal sheathing regions.
Identified sentence: 'Arber’s microscopic analyses of vascular bundle arrangement in Sagittaria species revealed, however, that while the distal leaf apex in certain taxa indeed derives from petiolar tissue, the basal sheathing regions develop from distinct foliar primordia that exhibit inversions in xylem-phloem orientation typical of true laminas.'
Explicit detail retrieval requires matching the precise target concept in the text.
2
Compare the contrast drawn in the text between the distal leaf apex and the basal sheathing regions.
Distal apex = derives from petiolar tissue; Basal sheathing regions = develop from distinct foliar primordia with xylem-phloem inversions typical of true laminas.
The question specifically asks how the basal sheathing regions differ from the distal leaf apex.
3
Match the identified explicit fact to the equivalent paraphrase among the choices.
The option stating that basal regions 'develop from distinct foliar primordia exhibiting xylem-phloem inversions characteristic of true laminas' is an exact semantic match.
GRE explicit detail correct answers rely on accurate paraphrasing of text facts without introducing unstated assumptions.

Key Concept

Explicit Detail Retrieval in Reading Comprehension
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Topics

Explicit Detail Retrieval

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