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Trillium List Support: T-List-04: Trillium Cotyledon Comparisons Purpose: Provide a forum to support T-List discussions with the posting of pictures and other Information.
TRILLIUM- L: The Trillium and Woodland Plants Discussion Group (A Link to the T-List) Trillium Bibliography: A comprehensive
Trillium bibliography compiled by the Trillium List people.
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Trillium Cotyledon Comparison or " why Trillium rivale has a broad leaf-like cotyledon" by John F. Gyer February 2006 Description of a trillium cotyledon and definitions: In trillium the cotyledon probably secretes enzymes that digest the endosperm. But the cotyledon definitely absorbs nutrients from the endosperm and later emerges from the seed husk as a photosynthetic organ. During the skotomorphogenic growth of a trillium seedling the cotyledon itself grows until only the absorptive tip remains in the seed husk. The emergent photosynthetic part of the cotyledon has been called the "hyperphyll". The young cotyledon, enclosed by the seed husk, and later the absorptive tip have been called "suctorial" ( because it sucks nutrition from the pool of digested endosperm) or more recently the "haustorium". My preference is "suctorial" because it emphasizes the absorptive function. Haustorium is in more current literature, but its origin is as a description of "root or root-like outgrowth in certain parasitic plants through which food is absorbed from the host". Since the triploid endosperm is not a host plant, but a dedicated food reserve for the seedling, and since the cotyledon is not root-like, and since "haustorium" is associated with parasitism, "haustorium" is a misleading descriptive term for the trillium cotyledon when it is enclosed in the seed husk. Discussion: The following pictures clearly show that the cotyledon can emerge from the seed husk flat or with edges curled or cupped to varying degrees. It is probable that the number of cotyledon blade cells is fixed just before or just after the hyperphyll of the cotyledon emerges from the seed husk. If future work shows this hypothesis true, then the width of the photosynthetic cotyledon results from the expansion of the volume of these pre-existing cells. In large seeded species, such as T.cuneatum, the cell divisions have room to expand without constriction by the seed husk. These emerge flat. Smaller seeds suffer more constriction and emerge cupped. Trillium rivale cotyledons are strongly curved within the cotyledon. There is only a small suctorial tip and it appears as if the entire cotyledon is suctorial until the endosperm is exhausted whereupon the cotyledon emerges and unfolds into a broad, blunt blade. Pictures: PICTURE 1: Trillium cuneatum, seedling with flat cotyledon. PICTURE 2: Trillium sessile, cupped cotyledon PICTURE 3: Trillium sulcatum, rolled emergent cotyledon PICTURE 4: Trillium erectum var. alba, rolled emergent cotyledon PICTURE 5: Trillium rivale (seed cross section), rolled suctorial cotyledon PICTURE 6: Trillium rivale excised suctorial cotyledon. YOUR PHOTOGRAPHS SUBMITTED FOR T-LIST DISCUSSIONS:
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