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Uploaded byNistarini College, Purulia (W.B) India
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Anomalous secondary growth in Plants with special reference to Bignonia, Boerhavia, Aristolochia & Dracaena

This document discusses anomalous secondary growth patterns in four plant species: Bignonia, Boerhaavia, Aristolochia, and Dracaena. In Bignonia, the cambium functions abnormally by producing secondary phloem in some segments while producing both phloem and xylem in others. In Boerhaavia, accessory cambium arise successively, producing concentric rings of vascular bundles. Aristolochia's cambium produces parenchyma instead of xylem and phloem between fascicular zones. Dracaena exhibits an anomalous cambium originating in the cortex that produces concentric secondary vascular bundles and conjunctive tissue, increasing stem thickness over time.

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WELCOME TO ANOMALOUS SECONDARY GROWTH w.s.r to Bignonia, Boerhavia, Aristolochia & Dracaena BY N.SANNIGRAHI, ASSOCIATE PROFESSOR, DEPARTMENT OF BOTANY, NISTARINI COLLEGE, PURULIA(W.B) INDIA
BRIEF IDEAABOUT ANOMALOUS SECONADRY GROWTH • Majority of the plants possess stelar structure of normal type but several of them are unusual structure that reflects ther common statement-Exceptions are the law of nature.This unusual structure differs from the usual types and therefore defined as anomalous.As a consequence, combinations of unusual structure, certain anomalous and extremely complex structure are formed termed as anomalies and this is very common in angiosperms. • These anomalies may be different reasons as follows: • 1.ANOMALOUS SECONDARY GROWTH IN DICOTYLEDONS • a. Anomalous position of cambium, • b. Abnormal beheaviour of normal cambium • c. Accessory cambium formation and its activity • d.Extrastelar Cambium • e,Interxylary phloem
SECONDARY GROWTH
ANOMALOUS SECONDARY GROWTH
CASUES OF ANOMILIES • 2. Absence of vessels in xylem, • 3. Scattered Vascular bundles in dicot, • 4. Presence of exclusive phloem and xylem bundles, • 5. Presence of medullary bundles, • 6. Presence of cortical bundles, • 7. Intraxylary Phloem, • 8. Vascular bundles arranged in ring in Monocots, • 9. Secondary growth in monocotyledons. • Those are the some of the important reasons deserve mentioning in order to address the anomalous beheaviour of the dicot stem in course of the secondary growth of the plant after the completion of the usual primary growth by the primary meristematic tissues of the plant body. • Examples: Bignonia, Securidaca, Bauhinia, Sarjania, Thinouia, Aristolochia, Bignonia, Bougainvillaea,Mirabilis, Boerhaavia, Tecoma, Amaranthus, Achyranthus,Chenopodium,CombretumStrychnos, Salvadora, PaperomiaCuscuta
Bignonia sp . Plant image
ANOMALOUS GROWTH IN Bignonia
How does anomaly develop in Bignonia ? • The anomalous growth in the secondary structure in Bignonia of Bignoniaceae is a typical example where Cambium normal in structure but functionis abnormal. • Here, the cambium function mostly in two ways- • 1. Certain segments of cambia cease to produce secondary xylem; instead of that, these segments of cambia donate secondary phloem only towards exterior. • 2. The other segments of cambia produce secondary phloem and secondary xylem by usual means-the secondary xylem more towards the centre and secondary phloem towards the periphery. • As a result, the woody cylinder appears to have ridges and furrows in longitudinally in stele.The ridges are wider than the grooves.The camium breaks up into a number of strips.The wider ones remain on the top of the ridges while narrower ones remain at their bases of the grooves.In the secodary phloem formed in the groove parallel strips of bast fibres are formed.
Development Pattern • This is a kind of adaptive anomaly having the arrangement of tissues from periphery to the centre in the following sequences: Cuticle-Epidermis- Hypodermis(Parenchyma-Starch sheath-Sclerenchyma)-Primary phloem- Cambia-Bast fibres interpolated-Phloem wedge-Secondarey xylem-Primary xylem-Pith • Bignonia is a woody climber-liane and the stem is twining and thus is inextensible as it hangs freely and has to bear its own weight. • The stem is also flexible as it has to withstand high velocity of wind and again subject to radial compression due to unequal growth in thickness for twining purposes. • For those reasons, the woody climber in the form of solid mass, instead of split into separate portions by the interpolations of the softer tissues into the woody mass to acheive inextensibility and flexibility. In Bignonia, softer phloem tissues is interpolated into the woody cylinder by the formation of grooves.
DIAGRAMATIC VIEW OF THE ANOMALOUS GROWTH
ANOMALOUS GROWTH IN Boerhaavia • In Boerhaavia, it is anomalous growth derived from the accessory cambium along with Bougainvillaea and Mirabilis.Several cambia arise successiuvely in centrifugal direction.Each cambia produces xylem and conjunctive tissuesto the inside and phloem & conjunctive tissue to the outside.The resulting tissue gives the concentric appearence of concentric rings of vascular bundles embeded in the conjunctive tissues. • According to P. Maheswari(1930) , the development of Boerhaavia dissusa is as follows: • The t.s of the vstem shows two medullary bundles-a middle ring oif 6-14 bundles and another ring of 15-20 or more bundles. • The bundles of middle ring increases in thickness to a limited extent by a fascicular cambium. • The bundles of outer ring are initially separate, quite small and each provided with its own fascicular cambium.
Boerhaavia sp plant
IMAGE OF SECONDARY GROWTH -ANOMALY
COMPARATIVE GROWTH PATTERN
MODE OF DEVELOPMENT • The fascicular cambia of the bundles become interconnected by interfascicular cambium of the bundles become interconnected by interfascicular cambial areas producing a cylindrical meristematic zone which gives rise to interfascicular parenchymatous or slightly prosenchymatous ground tissues between the bundles. • Thereafter, the cambium ceases to function and new meristem arises in the secondary parenchymatous or prosenchymatous tissue to which the first has given on the outside and the process repeats at interval. • Frequently, the successive cambia are ontogenetically interrelated , in the sister cells of one cambium layer become cambial cells of another layer.
Aristolochia sp. Plant
ANOMALOUS GROWTH IN Aristolochia
WHAT HAPPENS IN Aristolochia • Aristolochia, a dutchman's pipe is a climber belongs to Aristolochiaceae enjoys the anomalous secondary growth due to its climbing actvity.Here, the cambium is normal in structure but abnormal in function.The sequence of the growth pattern is as follows. • i. The cambial ring forms by the union of the interfascicular & fascicular bundles to form vascular cambial ring. • ii.The function of the vascular cambium ring becomes anomalous where the intrafascicular cut off xylem & phloem as usual external and internal side. • iii. but the interfascicular zone insted of giving xylem and phloem, it cuts off parenchymatous cells both on the inner and outer sides, thus they form like parenchyma. • The new cambial segments constantly form the rays of parenchyma, thus increasing the diameter.
STEPS FOLLOWED------------- • As the vascular cylinder, broken by wide rays, increases in circumference the cylinder of sclerenchyma that encircles the bundles bercome ruptured and the adjacent parenchyma grows intrusively into the gaps. • Eventually, a very fluted vascular cylinder is formed. • The species of aristolochia are woody climbers or lianes, which have diverse taxonomic affinities and often show anomalous structural features. • Among other characteriustics, the vessels are often unusually wide diameter. • Pith and medullary rays are crushed due to growth of secondary xylem. • After sometime, the pericycle breaks and the adjacent parenchyma cells invade to the breaks by the intrusive growth. • Thus, cambium normal in position but abnormal in function that reflects by its anomaly.
ANOMALOUS GROWTH IN Dracena sp.
About Dracena Plant & Growth Beheaviour • Some monocotyledons belonging to family, Liliaceae have arborescent habit with woody stems like Dracaena, Yucca, Cordyline, Agave, Aloe etc experiences another special type of secondary growth although the normal secondary growth is absent in monocot stems due to close vascular bundles.They exhibit an anomalous secondary growth in thickness producing a cambium-abnormal both in position and function. • Dracaena is a genus having 120 species belong to Agavaceae family under APGIV system of classification. The plant have special thickening called dracaenoid thickening due to abnormal beheaviour.Two type of species are found-wood tree like with cluster of leaves (D.fragrans) & rhizomatous (D.agolensis). • The anomalous secondary growth in this plant is an attraction of the anatomists due to following peculiar beheaviour which is reflected during its later stages of the growyth when the primary growth is over.
SECONDARY THICKENING • The following steps are followed in course of anomalous secondary thickenings: • i.Secondary growth is initiated by the special meristematic zone in the inner cortical region of the stem or very often from pericyle. • ii.A multilayered cambial cells formed from the inner cortical cells lying outside the vascular bundles. • iii. The cambium is formed in the region of the stem where the growth has been ceased. • iv. A large number of cambial cells in the inner side and small number on the outer sides. • v.The cells produced to the external side of the cambia are parenchymatous. • vi.The cells produced to the internal side are partially parenchymatous and partially vascular in nature remain separated from each other by lignified tissues and sometimes the tissue remains unlignified and thin walled. • vii.The parenchymatous cells produced internally to the cambia devloped into lignified conjunctive tissues
MICROSCOPIC IMAGE OF T.S UNDER MICROSCOPE
STEPS FOLLOED IN COURSE OF ANOMALY • viii.The vascular tissues produced internal to the cambium are vascular in nature and the vascular bundles are become concentric amphivasal type.This is formed due to the anticlinal divisions followed by periclinal division and even haphazardly to form xylem and phloem of the sercoindary bundles. • The small amount of phloem consist of short sieve tubes, companion cells and phloem parenchyma and the xylem is made of only tracheids, usually with sclariform thickening and small amount of xylem parenchyma with lignified walls. • The cambium add small amount of parenchyma cells outside and the primary vascular bundles appear larger. • The secondary bundles are smaller in size but more numerous in number. • It is to be remembered that in Dracaena, anomalous secondary thickening is brought about by a special cambium-secondary thickening meristem.Due to its actvity, conjunctive tissues and secondary vascular bundles originate.Contiuous formation of secondary tissues results in the increase in diameter even the girth of 45 feet (D.draco) with height of 70 feet of about 1000 years old.
ANATOMY OF Dracaena sp.
CONCLUSION • In Dracaena, no typical periderm formation by the activity of phellogen is found but storied cork cells are formed by the continuous periclinal division of the outermost cortical cells followed by the suberisation of the walls.Thus, storied cork cells form special mtype of protective layer outside the stem. • Thus, from the above discussion it is quite clear that anomalous forms of secondary growth into two categories-adaptive and non-adaptive.In contrast to the non-adaptive, anomaly is not an adaptation to definite external condition but it represents variations in design.The exception is the law of the nature- it has been reflected in terms of the anomalous secoindary growth as found in the different type of plants as you have gone through the anatomy of Bignonia, Boerhaavia, Aristolochia and last but not least in Dracaena.
EXCEPTIONS-THE RULE OF NATURE
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