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Telome theroy

This document summarizes the Telome Theory, which proposes that all vascular plants evolved from a simple leafless ancestral plant called Rhynia. The theory describes how evolutionary processes like overtopping, reduction, planation, syngenesis, and curvation acted on the telomes (terminal branches) of this ancestor to produce the diversity of plant forms seen today. It provides details on these processes and how they led to the formation of leaves, stems, and other structures. While pioneering, the theory is criticized for not fully explaining the origin of microphyllous leaves in lycophytes and for lacking evidence in its application to some plant groups.

Education◦
Telome Theroy Presented by :- Prajapati Jinal V. M.Sc Sem – 1 (botany) CBO :- 402 Department of life sciences, H.N.G.U. , Patan
Content • Introduction • Meaning of Telome Theory • Process of Telome Theroy • Merits & Demerits
Introduction • This theory was first proposed by Walter Zimmermann in 1930 . • This theory is based on fossil record and synthesizes the major steps in the evolution of vascular plants. • According to this theory, all vascular plants evolved either directly or indirectly from a simple leafless Rhynia type ancestral from made up of sterile and fertile axes.
Meaning of Telome Theroy • A Telome is defined as “ the single – nerved ultimate terminal portion of a dichotomising axis.” • I.g :- It is the point of the most distal dichotomy to the tip of a branch. The connecting axes between dichotomies are called mesomes. • Functionally , Telome are two types… 1. Fertile Telome 2. Sterile Telome
Process of Telome Theroy • According to Zimmermann, these Telomes of primitive Rhynia type of vascular plants have been subject to certain evolutionary process in varying degrees among the taxonomic groups. • These evolutionary process are :- 1. Overtopping 2. Reduction 3. Plantation 4. Syngenesis 5. curvation
1 . Overtopping • In this process one of the two dichotomising branches of the primitive axis produced by the apical meristem outgrows or overgrows the other. • The larger axis thus produced become the stem, while the shorter or overtopped branches represent the beginning of lateral branches or leaves .
2 . Reduction • In this process , the activity of terminal meristem of each Telome of the truss becomes suppressed resulting into much shorter branches by decreasing the length of Telome and mesomes • This process is responsible for the formation of microphyllous leaves of the lycopsida and sphenopsida as well as the needle like leaves of conifers .
3 . Planation • The process of Planation caused the Telome and mesomes of the truss to shift a three dimensional pattern to a single plane . • The process of infilling with photosynthetic and other tissues between the plannated branches is called webbing which have led to the evolution of flattened leaf like structure with a dichotomously veined lamina .
4 . Syngenesis ( webbing ) • This is an evolutionary process Where tangential fusion of Mesomes and Telome takes place . • The lateral fusion of sterile vegetative Telome and mesomes resulted into complex Anastomosing vascular systems in stem.
5 . Curvation • This evolutionary process is caused due to the unequal growth of the tissues on two opposite flanks of the Telome. • It has two sub processes :- 1 . Recurvation 2. incurvation
A . Recurvation • In this sub processes the Telome bends inward an axis. • The inward projecting sporangia on a sporangiophore of Equisetum the result of this sub process .
B . Incurvation • In this sub process, the fertile Telome bends downward resulting in the downward shifting of the sporangia from terminal to the ventral surface of the leaf .
Merits of the Telome Theory • It is outcome 0f a master mind that has portrayed , in a skilful manner the origin and evolution of the saprophytes of land plants. • Many of his assumptions are correct and based on exact phyletic relationships between the varions groups of plants both living and extinct. • It explains in a nice manner that the entire saprophytes is an axis that has an underground portion called the root and an aerial part called the shoot .
Demerits of the Telome Theory • The Theory is open to criticism in its application to the origin of lycophyta . • The origin of microphyllous leaves of the lycophyta by reduction of the Telome trusses is not exemplified by any living or extinct vascular plant . • Zimmermann scheme for the pteropsida or at least some pteropsida , has much supporting evidence .
Reference • Ptridophyta By - s.k .Singh  www. Biologydiscussion.com
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