sailent features of cordaitean stem.
Answers
Answer:
The spherical coordinate system is commonly used in physics. It assigns three numbers (known as coordinates) to every point in Euclidean space: radial distance r, polar angle θ (theta), and azimuthal angle φ (phi). The symbol ρ (rho) is often used instead of r.
Explanation:
1. Poroxyleae:
This had a single genus known as Poroxylon. Here the stem was slender with long internodes and within the stem were collateral exarch primary bundles, the pith was large, and double leaf traces for each leaf which had thick parallel venation in it.
2. Pityeae:
It included a single genus Pitys where the bundles were mesarch, the wood was with multi-ciliated pits, so it differed from Cordaiteae having mesarch bundles.
3. Cordaiteae:
It included a number of genera. The best known genus was Cordaites.
Features of Cordaitales of Cordaitales:
(A) Morphological Features:The plant was tall and slender. It had a crown of branches near the top, leaves were large simple and pendulate and not found in any living gymnosperms.
The plant was tall and slender. It had a crown of branches near the top, leaves were large simple and pendulate and not found in any living gymnosperms.(B) Anatomical Features:
The plant was tall and slender. It had a crown of branches near the top, leaves were large simple and pendulate and not found in any living gymnosperms.(B) Anatomical Features:The internal structure of stem in Cordaites showed a combination of Cycas and conifers characters. Pith like cycads layer but discoid in form, i.e., it was in form of plates at intervals. The vascular cylinder was like those of conifers. It was made up of thick collateral endarch primary bundles which sometimes however, seem to have been mesarch as in Mesoxylon.
The plant was tall and slender. It had a crown of branches near the top, leaves were large simple and pendulate and not found in any living gymnosperms.(B) Anatomical Features:The internal structure of stem in Cordaites showed a combination of Cycas and conifers characters. Pith like cycads layer but discoid in form, i.e., it was in form of plates at intervals. The vascular cylinder was like those of conifers. It was made up of thick collateral endarch primary bundles which sometimes however, seem to have been mesarch as in Mesoxylon.There was good deal of normal secondary growth. Secondary xylem was made up of living pitted tracheids with pits on radial walls. In fact it is clear that majority of plants found in Carboniferous period belonging to Cycadofllicales, Cordaitales and a number of fossil pteridophytes. The stems had good deal of secondary growth in them, but in these no annular rings.