Module 12 - Secondary Growth Flashcards
(41 cards)
Wood is composed of?
Secondary Xylem
3 planes of view of wood
Tangential, radial, and transverse
Vessel members that transport materials longitudinally
Axial system
Transports materials radially
Ray system
Types of rays
Multiseriate - marami cells
Uniseriate - isang line ng rays lang
Structure of bark that permits the passage of gas inward and outward of the plant
Consists of loosely packaged parenchyma cells
Living, require oxygen
Lenticels
Parts of the periderm
Cork (Phellem)
Cork Cambium (Phellogen)
Phelloderm
- increase in length of the shoot and the root
- the result of cell division in the apical meristems and elongation of cells
1°ry Growth
- characterized by an increase in thickness or girth - caused by cell division in the lateral meristems
2°ry Growth
mostly undergo 1°ry growth, with little 2°ry growth
Herbaceous plants
- 2°ry growth produces wood (dicots & gymnosperms, rarely in monocots)
- No 2°ry growth in Lycophyta and Pterophyta
Woody plants
- Found exclusively in roots and stems.
- Responsible for secondary growth, leading to an increase in the girth of the organ.
- Classified as secondary meristems, as they develop entirely or partly from differentiated tissues.
Lateral Meristem
gives rise to secondary xylem and phloem
Vascular Cambium
Gives rise to cork and phelloderm
Cork Cambium
Conditions for the origin of vascular cambium
- If all procambial cells differentiate into primary vascular tissues, no vascular cambium is formed.
- If some procambium remains in a meristematic state after primary growth, it becomes the vascular cambium.
- Vascular cambium may also originate from differentiated tissues, such as pericycle and interfascicular parenchyma, not just residual procambium.
portion of the vascular cambium that develops within the vascular bundles; it originates from residual procambium
Fascicular Cambium
portion of the vascular cambium that develops between the vascular bundles; it originates from interfascicular parenchyma
Interfascicular Cambium
- Cells divide anticlinally to produce more cambial cells.
- Cells divide periclinally; the inner cell differentiates into secondary xylem, while the outer cell differentiates into secondary phloem.
Vascular Cambium Cells
Gives rise to 2°ry Xylem inward & 2°ry Phloem outward
Vascular Cambium
2 Cell Types in the Vascular Cambium
- Fusiform initials - tall, axially oriented cells; give rise to the axial xylem and phloem
- Ray initials – smaller, round to angular in shape; give rise to xylem and phloem rays
- Both are densely cytoplasmic with thin bodies
It serves as a protective tissue, replacing the epidermis.
In herbaceous dicots, it is typically limited to the oldest parts of the root or stem.
Monocots usually lack a well-developed protective tissue, often having storied cork or none at all.
It is a component of the bark, constituting all tissues outside the vascular cambium.
Periderm
cork cambium, a lateral meristem, unlike vascular cambium has only 1 type of initial cells.
In stems, it can arise from epidermis, cortex or phloem and in roots, from the pericycle
Produces the periderm
Outer product is the cork/phellem, inner product is the phelloderm
Phellogen
Arranged in compact rows without intercellular spaces.
Primary wall composed of cellulose, sometimes with lignin or suberin.
The suberin layer is impermeable to gases and water, resistant to the action of acids.
Ultimately, these cells become dead.
Phellem
Living cells with non-suberized walls.
Some parenchyma cells may store starch.
In certain cases, parenchyma cells contain chloroplasts and are photosynthetic.
Sclereids may be present in some parenchyma tissues.
Phelloderm
