Baggett, Nikole (2012) Encyclopedia of extinct plants. University Publications, Delhi, India. ISBN 9788132337416
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Abstract
Cooksonia is an extinct grouping of primitive land plants. The earliest Cooksonia date from the middle Silurian, about 425 million years ago, the group continues to be an important component of the flora until the early Devonian. For historical reasons, while Cooksonia fossils are distributed globally, most type specimens come from Britain. Only the sporophyte phase of Cooksonia is currently known. Individuals were small, a few centimeters tall, and had a simple structure, they lacked leaves, flowers and roots although it has been speculated that they grew from an unpreserved rhizome. They had a simple stalk, that branched dichotomously a few times. Each branch ended in a sporangium, a rounded, spore-bearing structure. Specimens of one species of Cooksonia have a dark stripe in the center of their stalks, which has been interpreted as the earliest remains of water carrying tissue. Other Cooksonia species lacked such conducting tissue. Cooksonia specimens occur in a range of sizes, and varied in width from -0.03 to 3 mm. Specimens of different sizes were probably different species, not fragments of larger organisms: fossils occur in consistent size groupings, and sporangia and spore details are different in organisms of different sizes. The organisms probably exhibited determinate growth. Some Cooksonia species can be shown to bear stomata, which had a role in gas exchange, this was probably to assist in transpiration-driven transport of solutes in the xylem, rather than primarily in photosynthesis, as suggested by their concentration at the tips of the axes. These clusterings of stomata are typically associated with a bulging in the axis at the neck of the sporangium, which may have contained photosynthetic tissue, reminiscent of some mosses.
| Item Type: | Book |
|---|---|
| Subjects: | S Agriculture > SB Plant culture |
| Divisions: | Electronic Books |
| Depositing User: | Esam @ Hisham Muhammad |
| Date Deposited: | 12 Feb 2023 06:49 |
| Last Modified: | 12 Feb 2023 06:49 |
| URI: | http://odlsystem2.utm.my/id/eprint/4003 |
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