Anomalous Secondary Growth
In most of the angiosperms normal secondary growth takes place. But many dicotyledons show deviation from the normal type of secondary growth. The growth which is in contrast to the normal secondary growth is known as the abnormal or anomalous secondary growth.
Anomalous secondary growth is commonly seen in tropical plants than in temperate plants.
Haberlandt recognized two types of anomalous secondary growths
- adaptive
- non-adaptive.
The anomalous secondary growth that takes place due to its functional requirements is called adaptive secondary growth. It takes place to fulfil the mechanical requirements of the plants as per their morphological requirements as per their morphological structure e.g., Aristolochia, Bignonia, Draceana.
The anomalous secondary growth that takes place due to environmental requirements and has no functional significance to the plants is called as non-adaptive secondary growth. Eg., Amaranthus, Achyranthes, Boerhaavia.
Usually, secondary growth does not take place in monocotyledonous plants. However, certain monocots are arborescent plants. To suit to their woody habit and to produce a strong stem, anomalous secondary growth occurs in these plants; e.g., Yucca, Agave, Dracaena.
In storage roots to produce the required tissue to store the food, adaptive type of anomalous secondary growth takes place; e.g., Beta vulgaris, Daucus carota etc.
Anomalous secondary Growth in Achyranthes Stem
The young stem has a wavy outline with alternate ridges and furrows.
Epidermis: Made up of single row of tubular cells. The cells are closely arranged with thick outer walls coated with lignin, followed by cutin. Several multicellular hairs are present over the cells of the epidermis.
Cortex: The peripheral hypodermal region is made up of collenchymas below the ridges and chlorenchyma below the furrows.
Endoermis: consists of single row of tangentially elongated parenchyma cells.
Pericycle: Made up of sclerenchyma, parenchymatous cells are also present.
Vascular Bundles: arranged in form of a ring. They are conjoint, collateral, endarch and open. Medullary rays are present between the vascular bundles.
Apart from the primary vascular bundles, two medullary vascular bundles are present in the pith region. The medullary vascular bundles are conjoint, collateral, endarch and closed. These two bundles lie and grow opposite to each other.
Secondary Growth and Medullary Bundles:
In the pericycle region, extrastelar cambium strips develop which produce secondary vascular bundles. Cambium also produces the conjunctive tissue between the vascular bundles. the conjective tissue present between the xylem and phloem become sclerenchymatous. due to this it appears secondary phloem become surrounded by xylem. Secondary vascular bundles and conjunctive tissues are present without any sharp limits. So phloem of the secondary vascular bundles appears in the form of patches. This phloem is the included phloem.
The anomalous secondary growth that takes place due to environmental requirements and has no functional significance to the plants is called as non-adaptive secondary growth. Eg., Amaranthus, Achyranthes, Boerhaavia.
Usually, secondary growth does not take place in monocotyledonous plants. However, certain monocots are arborescent plants. To suit to their woody habit and to produce a strong stem, anomalous secondary growth occurs in these plants; e.g., Yucca, Agave, Dracaena.
In storage roots to produce the required tissue to store the food, adaptive type of anomalous secondary growth takes place; e.g., Beta vulgaris, Daucus carota etc.
Anomalous secondary Growth in Achyranthes Stem
The young stem has a wavy outline with alternate ridges and furrows.
Epidermis: Made up of single row of tubular cells. The cells are closely arranged with thick outer walls coated with lignin, followed by cutin. Several multicellular hairs are present over the cells of the epidermis.
Cortex: The peripheral hypodermal region is made up of collenchymas below the ridges and chlorenchyma below the furrows.
Endoermis: consists of single row of tangentially elongated parenchyma cells.
Pericycle: Made up of sclerenchyma, parenchymatous cells are also present.
Vascular Bundles: arranged in form of a ring. They are conjoint, collateral, endarch and open. Medullary rays are present between the vascular bundles.
Apart from the primary vascular bundles, two medullary vascular bundles are present in the pith region. The medullary vascular bundles are conjoint, collateral, endarch and closed. These two bundles lie and grow opposite to each other.
Secondary Growth and Medullary Bundles:
In the pericycle region, extrastelar cambium strips develop which produce secondary vascular bundles. Cambium also produces the conjunctive tissue between the vascular bundles. the conjective tissue present between the xylem and phloem become sclerenchymatous. due to this it appears secondary phloem become surrounded by xylem. Secondary vascular bundles and conjunctive tissues are present without any sharp limits. So phloem of the secondary vascular bundles appears in the form of patches. This phloem is the included phloem.
