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Psilotum is a genus of fern-like vascular plants.It is one of two genera in the family Psilotaceae commonly known as whisk ferns, the other being Tmesipteris.Plants in these two genera were once thought to be descended from the earliest surviving vascular plants, but more recent phylogenies place them as basal ferns, as a sister group to Ophioglossales.
Date/Time Thumbnail Dimensions User Comment; current: 14:47, 17 November 2022: 1,405 × 811 (457 KB): TheBartgry: Reverted to version as of 00:21, 10 December 2012 (UTC) showing continuity between nuclear membrane and ER is useful
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A central strand of xylem occupied up to a third of the diameter of the stem. In the lower parts of main stems it was circular, enlarging before it divided prior to dichotomous branching. Higher up it became elliptical in cross-section, corresponding to the two rows of fertile branching units.
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Pteridophyte life cycle. Just as with bryophytes and spermatophytes (seed plants), the life cycle of pteridophytes involves alternation of generations. This means that a diploid generation (the sporophyte, which produces spores) is followed by a haploid generation (the gametophyte or prothallus, which produces gametes). Pteridophytes differ ...
Helianthus stem in section. The cells of the vascular cambium (F) divide to form phloem on the outside, located beneath the bundle cap (E), and xylem (D) on the inside. Most of the vascular cambium is here in vascular bundles (ovals of phloem and xylem together) but it is starting to join these up as at point F between the bundles.
Vegetative stem: N = node, I = internode, B = branch in whorl, L = fused microphylls Cross-section through a strobilus; sporangiophores, with attached sporangia (spore capsules) full of spores, can be discerned. Strobilus of E. braunii, terminal on an unbranched stem