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Questions and Answers
The secondary xylem consists of two systems: the horizontal system and the ______ system.
The secondary xylem consists of two systems: the horizontal system and the ______ system.
vertical
Ray parenchyma originates from the cambial ray ______.
Ray parenchyma originates from the cambial ray ______.
initials
Axial parenchyma can be distributed in an ______ manner where its distribution is independent of the vessels.
Axial parenchyma can be distributed in an ______ manner where its distribution is independent of the vessels.
apotracheal
Terminal parenchyma forms at the end of the growth ______ in the form of single cells or continuous layers.
Terminal parenchyma forms at the end of the growth ______ in the form of single cells or continuous layers.
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Both the height and width of the ray are determined in ______ sections.
Both the height and width of the ray are determined in ______ sections.
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Initial parenchyma cells formed at the beginning of the growth ring are in the form of single cells or continuous ______.
Initial parenchyma cells formed at the beginning of the growth ring are in the form of single cells or continuous ______.
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Scanty paratracheal parenchyma forms an incomplete ______ around the vessel.
Scanty paratracheal parenchyma forms an incomplete ______ around the vessel.
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Tyloses are outgrowths that penetrate through the pits into the lumen of ______ or tracheids when they become inactive.
Tyloses are outgrowths that penetrate through the pits into the lumen of ______ or tracheids when they become inactive.
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Secondary phloem elements have a similar arrangement to that of the secondary ______.
Secondary phloem elements have a similar arrangement to that of the secondary ______.
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In conifers, the vertical system of secondary phloem comprises sieve cells, phloem parenchyma, albuminous cells and phloem fibers.
In conifers, the vertical system of secondary phloem comprises sieve cells, phloem parenchyma, albuminous cells and phloem fibers.
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Study Notes
Secondary Xylem Structure
- Secondary xylem is divided into two systems: horizontal (ray system) and vertical (axial system).
- Horizontal system originates from ray initials, forming xylem rays.
- Vertical system originates from fusiform initials, comprising tracheary elements, xylem fibers and axial parenchyma.
- Xylem parenchyma consists of two types:
- Ray parenchyma originate from cambial ray initials.
- Axial parenchyma originate from cambial fusiform initials.
- Ray parenchyma stores starch, fats, tannins, and other substances.
- Ray length/width are determined by cross section, longitudinal sections (radial and tangential).
- Ray height is determined in both radial and tangential longitudinal sections.
- Ray parenchyma can extend into phloem and pith, becoming medullary rays.
Axial Parenchyma Types
- Axial parenchyma are categorized by distribution:
- Apotracheal: Independent of vessel distribution, further subdivided into:
- Diffuse: Axial parenchyma forms uniseriate strands or single cells, scattered irregularly.
- Banded/metatracheal: Parenchyma is in concentric bands.
- Terminal: Parenchyma cells formed at the end of the growth ring (single cells or layers).
- Initial: Parenchyma cells formed at the beginning of the growth ring (single cells or layers).
- Paratracheal: Associated with vessels, further divided into:
- Scanty: Parenchyma forms incomplete sheath around the vessel.
- Unilateral: Parenchyma occurs on one side of the vessel (external/internal).
- Vasicentric: Parenchyma forms complete sheath (circular or elliptical) around the vessel.
- Aliform: Parenchyma forms complete sheath with lateral wing-like extensions.
- Confluent: Aliform parenchyma forms diagonal or tangential bands.
- Apotracheal: Independent of vessel distribution, further subdivided into:
Tyloses
- Xylem parenchyma is a significant part of woody plant xylem.
- It stores materials and facilitates radial water transfer between xylem and phloem.
- Ray and axial parenchyma play a role in defending against fungal pathogens.
- Parenchyma cells are often connected to xylem vessels/tracheids via pits.
- In some plants, parenchyma cells can form growths penetrating the vessel lumen.
Secondary Phloem
- Secondary phloem structure is similar to secondary xylem.
- Vertical system originates from fusiform initials and includes sieve elements, phloem parenchyma, and phloem fibers.
- Horizontal system originates from ray initials and consists of phloem ray parenchyma.
- Secondary phloem, like secondary xylem, can be either storied or non-storied, and often exhibits annual growth rings.
- In conifers, the vertical system includes sieve cells, phloem parenchyma, albuminous cells, and phloem fibers. Phloem rays are largely composed of parenchyma, sometimes with albuminous cells.
- In dicots, the vertical system includes sieve-tube members, companion cells, axial parenchyma, and xylem fibers. The horizontal system consists of uniseriate, biseriate, or multiseriate rays, composed of parenchyma cells.
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Description
Explore the intricacies of secondary xylem, focusing on its horizontal and vertical systems. Understand the roles of ray and axial parenchyma, and learn how different types contribute to the overall functionality of the xylem. This quiz will test your knowledge on xylem anatomy and its components.
