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In Pinus, needle vascular bundles are
A) Conjoint collateral and open
B) Collateral and closed bicollateral
C) Amphicribral
D) Radial

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Last updated date: 13th Jun 2024
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Answer
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Hint: The young stem of Pinus resembles the anatomy of a dicotyledonous stem in many respects. The overall arrangement of the assorted tissues from the circumference to the centre is the same. However, it differs, from the dicot stem in having an oversized number of resin ducts crammed with resin.

Complete answer:
The epidermis has an irregular outline. Endodermis and pericycle is similar to dicotyledonous stem, but the sclerenchyma is absent in pericycle. The vascular bundles aren't wedge-shaped, as within the dicotyledons. Phloem consists of annular and spiral tracheids which are dispersed irregularly towards the centre. Meta-xylem consists of tracheids with bordered pits. The tracheids are arranged in radial rows as seen within the transverse section of the stem. The pits of the pine wood are large and present around the radial walls. There aren't any true vessels.

i) Vascular bundles: These are collateral and closed, and arranged during a ring, as in dicot stem which consists of phloem, cambium and xylem.
ii) Phloem: The phloem consists of sieve tubes and phloem parenchyma, but no companion cells. It is present on the outer side of the bundle.
iii) Cambium: it consists of layers of thin walled, rectangular cells present in between xylem and phloem.
iv) Xylem: It consists exclusively of tracheids; there aren't any true vessels.
Resin ducts are present here. Protoxylem lies towards the centre and consists of some annular and spiral tracheids which don't seem to be disposed of in any regular order.
Metaxylem is present towards the cambium and has tracheids with bordered pits which develop on the radial walls. The tracheids are four sided and are arranged in definite rows.

Therefore, the correct answer is ‘B’, i.e, collateral and closed bicollateral.

Note: The secondary growth in the pine stem takes place in barely the identical way as during a dicotyledonous stem. However, there are distinct annual rings, consisting of the autumn wood and spring wood. The phloem portion consists of middle starch cells, and upper and lower layers of protein containing cells, called albuminous cells. The xylem consists of comparable starch cells within the middle, and empty cells with bordered pits, called tracheid cells, within the upper and lower layers.