Q.48 Which one of the following families shows bicollateral vascular bundle in the transverse section of
the stem?
(A) Rutaceae
(B) Asteraceae
(C) Cucurbitaceae
(D) Malvaceae
Bicollateral vascular bundles feature phloem on both sides of xylem, with cambium strips, typically seen in certain dicot stems. The correct answer is (C) Cucurbitaceae. This trait aids efficient transport in climbing plants like cucumbers.
What Are Bicollateral Bundles?
Bicollateral vascular bundles contain outer phloem, outer cambium, xylem, inner cambium, and inner phloem, making them open and capable of secondary growth. These differ from collateral bundles, where phloem lies only outward from xylem. Plants with bicollateral bundles often belong to specific angiosperm families adapted for vigorous growth.
Option Analysis
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(A) Rutaceae: Features collateral vascular bundles, typical in citrus family stems, lacking inner phloem.
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(B) Asteraceae: Shows concentric or collateral bundles in herbaceous stems, not bicollateral.
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(C) Cucurbitaceae: Exhibits bicollateral bundles in stem transverse sections, as in Cucurbita, with phloem flanking xylem.
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(D) Malvaceae: Contains collateral bundles, common in cotton family, without dual phloem layers.
Why Cucurbitaceae Stands Out
Cucurbitaceae stems display bicollateral bundles prominently in transverse sections, supporting tendril climbers’ rapid expansion. This anatomy enables repeated secondary growth via active outer cambium.
