The vase life of many flowers is limited by an occlusion in the stem, leading to premature symptoms of water stress. The occlusion can be due to numerous factors inherent in the stem, such as the outflow - upon cutting - of latex, gum, mucilage, and resin, the deposition of mucilage into xylem vessels by adjacent living cells, or the formation of tyloses. The latter are outgrowths of living cells into the lumen of xylem conduits. These forms of occlusion are highly dependent on the species. Two other types of vascular occlusion occur in all cut flowers: blockage due to bacterial growth and the one due to the formation of gas bubbles (emboli). The latter is due to cavitation in the stems. Although bacterial occlusion occurs in all flowers, various species and cultivars respond differently. Although cavitation may occur in all flowers, there is a difference between species and cultivars in the time until the number of cavitations is high enough to hinder water flow. The literature on vascular occlusion has recently been summarised (van Doorn, 1997). In order to avoid repetition, a few recent developments are discussed in some detail: a) the effects of water temperature, b) cavitation as a result of bacterial blockage, and c) the importance of cavitation repair.
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