Pentoxylon
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Pentoxylales were small trees or shrubs that existed in the Jurassic period in India. They had long and short shoots resembling Ginkgo, with spirally arranged leaves and scales. The stems (Pentoxylon) had five triangular segments around a central tissue. Leaves (Nipaniophyllum) were strap-shaped with a midrib. Male cones (Sahnia) bore pollen sacs on short shoots. Female cones (Carnoconites) had ovules aggregated into strobili on short shoots. Stomata were syndetochelic. Wood was pycnoxylic, resembling conifers. Pentoxylales displayed features intermediate between ferns
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Pentoxylon
- 2. PentoxylalisPentoxylalis Habit : small tress or shrubs that possessed long and short shoots. Stem : called Pentoxylon because it frequently showed five segments of triangular vascular tissue arranged in a ring around a central ground tissue. The primary xylem is mesarch and secondary xylem is pycnoxylic ring around a central ground tissue. The primary xylem is mesarch and secondary xylem is pycnoxylic (resembling the wood of conifers). The short and long shoot are covered by an armour of spirally arranged leaf bases. The short shoots often terminated in a crown of spirally arranged Nipaniophyllum-type of leaves. Besides foliage leaves some short shoots were terminated by clusters of ovulate cones or pollen organs.
- 3. Discovery of Pentoxylales: This group has been discovered and named as “Pentoxyleae” by well-known Indian Palaeobotanist Professor Birbal Sahni (1948). This is a group of some fossil plants described from Rajmahal Hills in Amrapara District (Santhal Parganas) of Eastern Bihar (India) revealing their existence inEastern Bihar (India) revealing their existence in Jurassic Period.
- 5. Pentoxylon (stem), Short- & long-shoot morphology (like Ginkgo) 3mm to 2 cm diameter Each stele had its own cambium. The cambium was uniformly active in the young stems, but at maturity more secondary tissue developed towards the centre, and thus the secondary wood appeared eccentric. Eustele reminiscent of Medullosa. The primary xylem is mesarch and secondary xylem ispycnoxylic (resemblingmesarch and secondary xylem ispycnoxylic (resembling the wood of conifers). in five or six wedges around mesarch primary xylem strand (Pentoxylon) The short and long shoot are covered by an armour of spirally arranged leaf bases. The short shoots often terminated in a crown of spirally arranged Nipaniophyllum-type of leaves. Besides foliage leaves some short shoots were terminated by clusters of
- 6. Nipaniophyllum (leaf)- Leaves : are petiolate strap-shaped with prominent midrib closely resembling form-genus Taeniopteris in general features. However, structurally preserved leaves have been called NipaniophyllumHowever, structurally preserved leaves have been called Nipaniophyllum Foliage arises from short shoots, where leaf scars are commonly visible Leaves long, narrow (Taeniopteris) Syndetocheilic stomata Prominent mid-rib Secondary veins arising at right angles and unbranched to the leaf margin
- 7. Sahnia (male flower Sahnia nipaniensis) Pollen organs born in clusters on short shoots.They were present terminally on the shoot, and fused basally in a shallow disc .Vishnu-Mittre (1953) reported as many as 24 such pollen-bearing organs It consisted of a receptacle from whose rim like collar arose.numerous microsporophylls or microsporangiophores.The stalks gave rise to secondary laterals that terminated in several arose.numerous microsporophylls or microsporangiophores.The stalks gave rise to secondary laterals that terminated in several stalked pollen sacs Each microsporophyll possessed many pear-shaped, unilocular sporangia.The terminal position of the sporophyll was also occupied by a sporangium The sexine of the pollen wall is homogeneous while its nexine is present in the form of thin dark zone. In the region of aperture, the sporoderm is highly folded.Taylor & Taylor (1987) observed a few lamellae in the region of aperture. Other details of the male flowers are not yet fully known.
- 8. Carnoconites (female cone) C. compactum and C.laxum Ovules aggregated into strobili,They were mulberry-like, and attained a length of about 1.8 cm in Carnoconites compactum and 3 cm in C. laxum.They were, however, narrower in C. laxum. Attached to short shoots Unisexual (maybe too specialized to be ancestor to angiosperms) About 20 sessile ovules were seen attached on the receptacle, and there were no inter-seminal scales.Any sporophyll-like structure was also not reported. In-spite of these facts Sahni (1948) used the word ‘cone’ for these structures.The ovules were covered by a single integument.The nucellus was free from the integumentOvules almost completely surrounded by cupule Integument has inner sclerenchymized layer and fleshy outer layer
- 9. pentoxylon Pentoxylon (stem), Short- & long-shoot morphology (like Ginkgo) Eustele reminiscent of Medullosa. The primary xylem is mesarch and secondary xylem ispycnoxylic (rese mbling the wood Nipaniophyllum (leaf), Foliage arises from short shoots, where leaf scars are commonly visible Leaves long, narrow (Taeniopteris) Sahnia (male flower) Pollen organs born in clusters on short shoots It consisted of a receptacle from whose rime like collar arose Carnoconites (female cone) Ovules aggregated into strobili Attached to short shootspycnoxylic (rese mbling the wood of conifers). Wood in five or six wedges around mesarch primary xylem strand (Pentoxylon) The short and long shoot are covered by an armour of spirally arranged leaf bases. Syndetocheilic stomata Prominent mid-rib Secondary veins arising at right angles and unbranched to the leaf margin collar arose numerous microspor ophylls or microsporangiophor es. The stalks gave rise to secondary laterals that terminated in several stalked pollen sacs. Unisexual (maybe too specialized to be ancestor to angiosperms) Ovules almost completely surrounded by cupule Integument has inner sclerenchymized layer and fleshy outer laye
- 10. Origin of stomata Haplochelic : Syndetochelic : In some gymnosperms, applied to a type of stoma in which the 2 guard cells are derived from a single mother cell and the subsidiary cells are derived from a different initial. Ephedra In some gymnosperms, applied to a type of stoma in which the 2 guard cells and the subsidiary cells are all derived from a single mother cell. Welwitschia
- 11. Manoxylic and pycnoxylic wood . Wood of Gymnosperms are classified into manoxylic or pycnoxylic.This classification is based on the amount of xylem cells in the wood Manoxylic :It is the non-compact wood with large amount of parenchyma, large pith and Pycnoxylic wood: compact strong wood with large amount of xylem cortex mixed with less amount of xylem tracheids or wood. Parenchyma cells filled with starch grain . Not important commercially as xylem is less thus less durable. Cycas tracheid and small amount of parenchymatous wood. important commercially as xylem is more thus heavily durable pinus