The latter was developed under the abscise of the European Commission DG Enterprise and presented in Brussels in 2004.
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Abscission of the hypanthium during development of a nectarine fruit A plant will abscise a part either to discard a member that is no longer necessary, such as a leaf during autumn, or a flower following fertilisation, or for the purposes of reproduction. Most deciduous plants drop their leaves by abscission before winter, whereas evergreen plants continuously abscise their leaves. Another form of abscission is fruit drop, when a plant abscises fruit while still immature, in order to conserve resources needed to bring the remaining fruit to maturity. If a leaf is damaged, a plant may also abscise it to conserve water or photosynthetic efficiency, depending on the 'costs' to the plant as a whole.
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The scape does not abscise (shed) during seed dispersal, with the exception of Cybistetes where it detaches at ground level. The seeds also lack an integument, but are endosperm-rich and partially chlorophyllous with cork- covering.
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Due to its high levels of rooting hormones, P. trichocarpa sprouts readily. After logging operations, it sometimes regenerates naturally from rooting of partially buried fragments of branches or from stumps. Sprouting from roots also occurs. The species also has the ability to abscise shoots complete with green leaves.
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The abscission is selective, and the chance of dropping leaves increases as the number of galls increase. A leaf with three or more galls was four times more likely to abscise than a leaf with one, and 20 times as likely to be dropped as a leaf without any galls.Williams, A.G., & T.G. Whitham (1986). Premature leaf abscission: an induced plant defense against gall aphids.
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Dead leaves are marcescent in juvenile palms, but abscise, naturally fall off the tree, neatly in adults. The inflorescence is infrafoliar and surrounded by a long, leathery spathe, which curls up on itself after abscission (due to drying out). The inflorescence stalk is long and elliptic in cross-section. The rachis is very short, long and bearing about 30–50 crowded, spirally arranged rachillae.
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As summer progresses, symptomatic leaflets eventually abscise, leaving behind the rachis, which too eventually falls from the plant. Symptoms can be confined to single or multiple branches, but over multiple years will spread throughout the plant. While the symptoms do not kill the trees, the weakened health leads to reduced yields over time. There are other causes of similar symptoms, such as pecan scorch mites and drought stress, thus a laboratory analysis is recommended when diagnosing the disease.
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Like most members of the white pine group, Pinus subgenus Strobus, the leaves ("needles") are in fascicles (bundles) of 5, or rarely 3 or 4, with a deciduous sheath. They are flexible, bluish-green, finely serrated, long, and persist for 18 months, i.e., from the spring of one season until autumn of the next, when they abscise. The seed cones are slender, long (rarely longer than that) and broad when open, and have scales with a rounded apex and slightly reflexed tip, often resinous.
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Despite the existence of multiple species of Stigmaria, our understanding of the underground organs is based primarily on the widespread species Stigmaria ficoides. The stigmarian organs originate from the base of the trunk as four major axes extending horizontally, leading to a relatively shallow rooting system. Lateral appendages are attached to each axis in a helical pattern. These appendages would abscise as the plant grew, resulting in the characteristic circular external scars of Stigmaria fossil specimens. Although these appendages are often called “stigmarian rootlets,” their helical arrangement and growth abscission are actually more characteristic of leaves than modern lateral roots.
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Vertical metamers are also suggested in some desert shrubs in which the stem is modified into isolated strips of xylem, each having continuity from root to shoot. This may enable the plant to abscise a large part of its shoot system in response to drought, without damaging the remaining part. In vascular plants, the shoot system differs fundamentally from the root system in that the former shows a metameric construction (repeated units of organs; stem, leaf, and inflorescence), while the latter does not. The plant embryo represents the first metamer of the shoot in spermatophytes or seed plants.
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