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and can be dispersed some distance and will retain its viability for several months until reaching a suitable substrate. In the case of Avicennia and Heritiera (a non-viviparous form producing large, woody, one to several seeded keeled fruits - Plate 3) the fruits have spongy outer layers which afford extra buoyancy.
The other non-viviparous forms Excoecaria and Acanthus have an exploding capsule releasing numerous seeds, and Lumitzera produces an indehiscent single-seeded fruit. In these forms seed dispersal and development follow the normal pattern.
Because of the reduced supply of oxygen in the mud, the mangroves require an additional air supply. Forms such as Avicennia produce lots of upright root branches called pneumatophores from their cable roots (Plate 4). These pneumatophores contain aerenchyma (Fig 3) (specialized cells with large air spaces between) so that air transfer can readily take place. Bruguiera (Fig 4) and Kandelia produce bends in their roots which push up above the substrate surface (knee joints). These knee joints are again rich in aerenchyma to facilitate the transfer of air. Both pneumatophores and knee joints have special areas of thin-walled cells at their surface (lenticels) for gaseous exchange.
At high tide, the water within the substrate is highly saline, and mangrove plants are adapted in several ways to overcome the problems of high salt concentrations in their internal tissues. Like halophytes in general (plants which grow where salt concentration is high), mangroves can tolerate relatively high internal salt concentrations (Table 2). In addition, however, some are “salt excluders” (e.g. Kandelia) and physiologically prevent the entry of salts into the root tissues by a special ultrafiltration method. Any excess salt in the tissues is removed by an active pump mechanism. These forms thus maintain a salt concentration in their tissues which is only about 10% of that found in the non-excluders.
Other (e.g. Avicennia (Fig 5) and Acanthus) are "salt excreters" and continually remove salt from their tissues via salt glands in their leaves; others (e.g. Bruguiera and Lumnitzera (Fig 8)) store salt in vacuoles or even in crystalline form in their leaves so that it is physiologically inactive and will be lost at leaf fall; while others use more than one method (e.g. Excoecaria stores salt crystals and is a...
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and can be dispersed some distance and will retain its viability for several months until reaching a suitable substrate. In the case of Avicennia and Heritiera (a non viviparous form producing large, woody, one to several seeded keeled fruits - Plate 3) the fruits have spongy outer layers which afford extra bonyancy.
The other non viviparous forms Excoecaria and Acanthus have an exploding capsule releasing numerous seeds, and Lumitzera produces an indehiscent single seeded fruit. In these forms seed dispersal and development follow the normal pattern
Because of the reduced supply of oxygen in the mud, the mangroves require an additonal air supply. Forms such as Avicennia produce lots of upright root branches called pneumatophores from their cable roots (Plate 4). These pneumatophores contain aerenchyma (Fig 3) (specialized cells with large air spaces between) so that air transfer can readily take place. Brugutera (Fig 4) and Kandelia produce bends in their roots which push up above the substrate surface (knee joints). These knee joints are again rich in arenchyma to facilitate the transfer of air. Both pneumatophores and knee joints have special areas of thin walled cells at their surface (lenticels) for gaseous exchange.
At high tide, the water within the substrate is highly saline, and mangrove plants are adapted in several ways to overcome the problems of high salt concentrations in their internal tissues. Like halophytes in general (plants which grow where salt concentration is high), mangroves can tolerate relatively high internal salt concentrations (Table 2). In addition, however, some are “salt excluders” (e.g. Kandelia) and physiologically prevent the entry of salts into the root tissues by a special ultrafiltration method. Any excess salt in the tissues is removed by an active pump mechanism. These forms thus maintain a salt concentration in their tissues which is only about 10% of that found in the non- excluders.
Other (e.g. Avicennta (Fig 5) and Acanthus) are "salt execreters" and continually remove salt from their tissues via salt glands in their leaves; others (e g. Bruguiera and Lumnitzera (Fig 8)) store salt in vacuoles or even in crystalline form in their leaves so that it is physiologically inactive and will be lost at leaf fall; while others use more than one method (e.g Excoecaria stores salt crystals and is a
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