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Adventitious has various meanings in various disciplines and in general usage. ''Adventitious'' is from the Latin root ''advenire'', meaning "to come or be superadded" and in correct English the meanings tend to have connections to accidental or casual occurrence. "...of the nature of an addition from without; supervenient, accidental, casual. People sometimes speak of an event or occurrence as being "random", when the word "adventitious", or perhaps "accidental", might be more strictly correct. ==Botany== In botany, ''adventitious'' refers to structures that develop in an unusual place. This part of the article discusses adventitious roots, buds and shoots, which are very common in vascular plants. ===Buds and shoots=== Adventitious buds develop from places other than a shoot apical meristem, which occurs at the tip of a stem, or on a shoot node, at the leaf axil, the bud being left there during the primary growth. They may develop on roots or leaves, or on shoots as a new growth. Shoot apical meristems produce one or more axillary or lateral buds at each node. When stems produce considerable secondary growth, the axillary buds may be destroyed. Adventitious buds may then develop on stems with secondary growth. Adventitious buds are often formed after the stem is wounded or pruned. The adventitious buds help to replace lost branches. Adventitious buds and shoots also may develop on mature tree trunks when a shaded trunk is exposed to bright sunlight because surrounding trees are cut down. Redwood (''Sequoia sempervirens'') trees often develop many adventitious buds on their lower trunks. If the main trunk dies, a new one often sprouts from one of the adventitious buds. Small pieces of redwood trunk are sold as souvenirs termed redwood burls. They are placed in a pan of water, and the adventitious buds sprout to form shoots. Some plants normally develop adventitious buds on their roots, which can extend quite a distance from the plant. Shoots that develop from adventitious buds on roots are termed suckers. They are a type of natural vegetative reproduction in many species, e.g. many grasses, quaking aspen and Canada thistle. The Pando quaking aspen grew from one trunk to 47,000 trunks via adventitious bud formation on a single root system. Some leaves develop adventitious buds, which then form adventitious roots, as part of vegetative reproduction; e.g. piggyback plant (''Tolmiea menziesii'') and mother-of-thousands (''Kalanchoe daigremontiana''). The adventitious plantlets then drop off the parent plant and develop as separate clones of the parent. Coppicing is the practice of cutting tree stems to the ground to promote rapid growth of adventitious shoots. It is traditionally used to produce poles, fence material or firewood. It is also practiced for biomass crops grown for fuel, such as poplar or willow. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Adventitiousness」の詳細全文を読む スポンサード リンク
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