Callistophytales

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The Callistophytales are an order of extinct group of plants the seed ferns. The genus Callistophyton probably grew in the understory of the Carboniferous forests.

Features

Vegetative characteristics

Callistophyton was a small, spreizklimmende plant. She had a major axis, leading off from the 50 cm long side branches, where were large, feathery leaves.

The largest preserved trunk has a diameter of approximately 3 cm. The pith is parenchymatous and slightly angular. It is surrounded by up to 13 axial bundles of the primary xylem. The bundle number varies depending on the position on the trunk and whether straight branch leaf traces. There are species with mesarchem and exarchem xylem ( it ripens from the middle to both sides, or from outside to inside ). The tracheids of Metaxylems are wire or tracheids have bordered pits. To the primary xylem is a broad zone of secondary xylem, which is up to 70 cells wide. Here the tracheids in rows of one to five cell width are arranged which are separated by wooden beams. The pits are limited to the radial cell walls and are slit-like. The cambium first produced only xylem, later in equal parts xylem and phloem. Location and appearance of the primary phloem are not known. The secondary phloem consists of sieve, phloem parenchyma and Phloemstrahlen. Amber inclusions in the sieving panels suggest callose plugs. The bark comprises an inner, parenchymatous layer and an outer layer of longitudinal fibers which are embedded in the parenchyma. In the bark cavities are scattered present, which are filled with an amber-colored substance. Similar secretion Caves are found in all plant organs of the genus. In the inner bark of a periderm is to recognize that forms the outer boundary tissue in older stems.

The vascular system of Callistophyton is interpreted as independent Axialbündel that run through the trunk and branch of which leaf traces. The leaf traces are at the petiole base in duplicate, to the tip then individually. Sitting little axillary buds or lateral branches at the nodes. The buds are enclosed by two opposite leaves or Cataphyllen, extending beyond the tip of the bud. Side branches have the same structure as the above-described stem axis.

The roots of Callistophyton are diarch. In older specimens they contain abundant secondary tissues, including periderm. The roots are adventitious and arise at the shoot axis in the axils of the buds or side branches.

A similar class as Callistophyton is Johnhallia from the Middle Pennsylvanian. There are strains with a Eustele with about one centimeter in diameter. The primary strain has five vascular strands. In each bundle, there is a core of parenchyma. The fronds are flat and stand in a 2/5-Phyllotaxis to the stem axis.

In Callistophyton the leaves are arranged spirally. The largest leaves are about 30 cm long. The fronds are pinnate twice to four times, the leaflets are flat, deeply lobed and narrowed at the base. Sometimes find multicellular hairs on the underside. The leaflets are morphologically similar to the closely the shape genus Sphenopteris.

Reproductive organs

The seeds are flattened and are referred to as Callospermarion. Where the seeds have been formed in the plant, is not known. In analogy to the pollen organs, it is believed that they were sitting at the bottom of the leaflets.

The seeds ( plants ) are from 0.8 to 5 mm long, in one level to 3.8, in the other to 2.0 mm wide. The integument contains two vascular bundles in wing-like extensions. The integument consists of three parts, the bulk of the seed coat consists of cells of the outer sarcotesta and secretion contains large caves. In Callistophyon pusillum the nucellus is grown only in the base region (at the chalaza ) with the integument. The distal end forms a bottle-shaped pollen chamber. In many regarded as immature seeds pollen grains were found by Vesicaspora type in the pollen chamber. Probably the ovules formed a resinous pollination drops, which helped capture the pollen, similar to the extant gymnosperms.

The pollen organs were sitting on the abaxial side ( underside ) of the small leaflets. Idanothekion glandulosum from the Middle Pennsylvanian consists of a ring of six to nine sporangia arranged around a central, leitbündelführende column and are fused in the proximal part. Each of these synangia is about one millimeter long and as wide. The sporangium is thick with the exception of the inward-facing wall is thin, and where the hole occurred. The vascular tissue is available as a broad band in the outer layers each sporangium. Callandrium callistophytoides has virtually the same structure, it only lacks the vascular tissue in the sporangium. Both pollen organs contain small ( about 40 microns ), monosaccate pollen grains, which are similar to those of conifers. As an individual finds the pollen grains would be placed in the form genus Vesicaspora. The pollen is bilaterally and at the equator has an elliptical outline. The body is surrounded by an equatorial air bag ( sac ), which is finely ornamented. Is an elliptic germ fold ( sulcus ) between the two lobes of the sac.

In pollen sacs developmental stages of Mikrogametophyten were observed to consist of two, three and four axially stacked cells. The proximal stationary cells are interpreted as prothallium cells, the largest cell as the embryonic cell or antheridium cell. The pollen was released at the 4- cell stage. The pollen was probably spread by the wind and caught by the fertilization of the ovules drops. The germination of the pollen carried on the sulcus located distally. In one case, a branched pollen tube an indication of a haustorium function of the pollen tube was observed in a seed plant, similar to the Cycadales. This would be a precursor to real Siphonogamie.

Documents

• Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants, pp. 550-558. Prentice Hall, Englewood Cliffs 1993. ISBN 0-13-651589-4

• Seed plants
• Spermatophytina
• Extinct plant