Short notes on the structure of a seive tube

Seive tubes are found in phloem. They are living cells and have the thin cellulose walls. In angiosperms there are enucleate while they are neucleate in gymosperms. The protoplast of seive tube has a big central vacuole which is filled with proteins. The cross wall between the seive tubes...
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What are the characters of tracheids are vessels?

Tracheids are dead cells and like sclerenchyma has neither the nucleus nor the phrotoplast. The lumin of cell is large. The wall of the tracheids is provided with a number of bordered pits. Taracheids have oblique end walls. They help in conduction and mechanical support. Vessles arise from traicheids...
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Which are the types of wall thickenings in xylem?

Annular: Lignin deposition is in form of annuli or rings. These rings are unconnected. The space between the rings is unthickened. Spiral: Lignifications occur in the form of a spiral band. Scalariform (ladder like): Wall thickening is in the form of transverse rods, very much resembling the rungs of...
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What are pits (in xylem); explain the types?

In xylem lignin deposition is uniform over the wall except for small porse, this porse are called pits. There are two types of pits viz., simple pit and bordered pit. A simple pit is just a opening in the wall. Whereas in a bordered pit the pit aperture is...
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Short notes on wood fibres and wood parenchyma

Wood Fibres: They are also called xylary fibres. Sclerenchyma fibres asĀ­sociated with xylem are termed wood fibres. They possess very thick walls and few small pits. They originate from the derivatives of the cambium and have varied shapes. In wood fibres, known as libriform fibres, the wall is extremely...
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What are sclerids? Mention their types

These are short isodiametric cells sometimes may be ilagulated also. Cell walls are thick and lignified. But the cells do not have tapering ends. The cells are dead and have a very narrow lumen. Sclereids are classified into the following types viz., brachysclereids or stone cells (short isodiametric dells...
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List the similarities and differences between sclerenchyma and xylem

1. Both are mechanical tissues. 2. In both the cell walls are thickened due to the deposition of lignin. 3. Both the tissues are dead at maturity. Differences: 1. Sclerenchyma is a simple tissue while xylem is a complex tissue. 2. Lignin deposition is uniform in sclerenchyma, while it...
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What are fibres? In which tissues are they found?

Fibres are elanguagated, selerenchyma cells with thick lignified walls the lumen is very narrow. Fibres offer mechanical support. Fibres are of three types surface fibres, wood fibres and bast fibres. Surface fibres are found distributed in the different parts of the plant among the paranchyma cells. Wood fibres are...
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What are the salient features of parenchyma?

Parenchyma cells are spherical or polygonal in shape. Sometimes they may be elongated and columnar as in the leaves. Studies based on geometric models have indicated that closely packed parenchyma cells have the shape of a polyhedron with approximately fourteen faces. Parenchyma cells are closely packed or arranged loosely...
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Notes on the features of Intercalary meristem

Intercalary meristems represent the detached portions of the apical meristems separated due to the growth of an organ. Intercalary meristems are always intermodal. In the early stages of development of the plant, whole or part of the intemode is meristematic. Subsequently a portion of it matures, as a result,...
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