An understanding of dormancy mechanisms is of ecological and economic importance. Identification of the level at which dormancy is imposed appears to be species specific. The variation brought about by this therefore requires that developmental studies be included in seed coat dormancy experiments. In most cases, a site of permeability can be identified during the developmental process, and this information can be utilized later to remove dormancy. Under natural conditions, the removal of seed coat dormancy requires the interaction of a number of ecological and physiological dormancy-breaking cues.

AbstractsDichrostachys cinerea seeds are impermeable to water and do not germinate readily . The plant, however, contributes to a bush encroachment problem, minimising visibility in wildlife reserves and reducing the area available for grazing . Natural dormancy-breaking conditions must therefore exist, promoting the germinability of these normally dormant seeds . Diurnal temperature fluctuations (50'C/15°C), especially when combined with moisture were found to break dormancy . High temperatures, such as those generated by fire, destroyed seeds . Seeds ingested by herbivorous browsers such as nyala, became permeable . Seed burial for 48 weeks, was a more effective treatment than storage in promoting permeability . Distribution of D . cinerea will therefore be restricted to areas in which these conditions or factors occur . Seeds germinated optimally at 30'C in the laboratory . 51

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The occurrence of very few seeds of Dichrostachys cinerea in the soil seed bank prompted the present study as to why animal browsers and seed predators should select the infructescence of this plant . The preferential and extensive browsing of this indehiscent legume is apparently not due to any exceptional nutritive value of the pods and seeds . However, it is probably the strong rich aroma of the infructescence which initially attracts animals to this food source . The structure of the infructescence, ensures that upon location a large number of pods and seeds are consumed . Ingestion of the pods will provide fibre, lipid, fatty acids, carbohydrates, amino acids, nitrogen and protein . 273 . IntroductionDichrostachys cinerea (L .) Wight et . Am is an indigenous legume invader of grasslands . The seed coat dormancy [10] is broken naturally by alternating temperatures (50/15'C), wet heat, seed burial and ingestion by herbivores [16] . Low numbers of Dichrostachys cinerea seeds were found in the soil seed bank suggesting that the seeds and/or pods are consumed, dispersed or rapidly and heavily predated .A large proportion (95%) of the seeds are lost to bruchid beetle damage . They are also eaten by rodents, black rhino, kudu, nyala, impala, cattle and duiker . Digestion by large mammals is not detrimental as action of gastric juices kills bruchid larvae and allows the seeds to remain viable provided there has not been any damage to the embryonic axis [15] . Seeds egested by large mammals (dispersal agents) have a greater probability of establishment as they end up in a microclimate conducive to germination . Bruchids and rodents are seed predators and destroy the seed .The pods of D . cinerea are indehiscent and collectively up to 40 pods form an infructescence which may attract browsers to the trees . It has not been established to what extent the browsers and seed predators benefit from consumption of pods and seeds of D . cinerea. This study was initiated to establish the nutritional value of the seeds and pods of D . cinerea . . Materials and methods .1 Plant materialMature green infructescences containing mature green seeds were collected from Mkuzi Game Reserve, Zululand . In the green pods, the seeds fill the pods whereas the mature brown seeds found in the brown, dry pods are much smaller . As the pods are indehiscent, animals will always consume both pods and seeds . The reproductive potential of D . cinerea was determined by collecting 30 infructescences and counting the number of pods per infructescence and the number of intact and predated (destroyed) seeds per infructescence . Pods and seeds were separated prior to chemical analysis . All