In equisetum carinal cavities are modification of
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Answer:
In equisetum carinal cavities are modification of primary xylem.
Explanation:
The first periclinal division in each segment from the apical cell of the stem separates pith and "primary cortex," which in turn gives rise to stele and cortex. 2. The pericycle, endodermis, and one or two layers of the inner cortex of the stem are stelar in origin. 3. Evidence is presented for regarding the so-called inner endodermis of the root as pericycle. 4. The endodermis and pericycle of the root are of cortical origin. 5. Dormant branches occur as in other species of Equisetum. They are exogenous in origin. 6. The first root developed by the branch is endogenous. 7. The stelar parenchyma in the root is much reduced. 8. Hydathodes of the water stomata type occur on the upper surface of the leaves. 9. Rare but well-developed tyloses are found in the carinal canals. 10. Reduction in xylem is extreme, the supranodal wood being frequently absent above the leaf traces, forming a gap in the xylem. 11. The gaps in the xylem of the cone are correlated with the size of the stele and failure of the fundamental tissue to develop.
The vascular bundles trifurcate at the nodes, with the central branch becoming the vein of a microphyll, and the other two moving left and right to merge with the new branches of their neighbours.The vascular system itself resembles that of the vascular plants' eustele, which evolved independently and convergently.Very rapid internode elongation results in the formation of a pith cavity and a ring of carinal canals formed by disruption of the primary xylem. Similar spaces, the vallecular canals are formed in the cortex.Due to the softer nature of the phloem, these are very rarely seen in fossil instances. In the Calamitaceae, secondary xylem (but not secondary phloem) was secreted as the cambium grew outwards, producing a woody stem, and allowing the plants to grow as high as 10m. All extant species of Equisetum are herbaceous, and have lost the ability to produce secondary growth.
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