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14C assimilates produced in a single shoot of a sand sedge plant proved to be translocated in the direction of the rhizome tip only. Labelled assimilates were found in all roots in the part of the plant system between the shoot administered with 14C02 and the rhizome tip, in the youngest shoot and in the rhizome tip itself. The percentage of assimilates exported by the mature shoots proved to be 30-35%. The amount of assimilates exported by the youngest shoot decreased from 22% in a I-shoot system to zero in the bigger plant systems. In the 5-shoot system also the export of the second youngest shoot started to decrease.In spite of the relatively great sink strength of the rhizome tip with regard to the assimilates exported by the nearby situated young shoots, the main source of assimilates for the rhizome tip proved to be the older shoots, lying at some distance. The ecological importance of this is that the rhizome tip will be able to cross unfavourable habitats, without the need for assimilates from the newlyformed shoots in those habitats.

SUMMARY The older shoots on the rhizome of the sand sedge have a lower waterpotential than the younger ones closer to the rhizome tip. The xylem translocation stream, that runs through the rhizome in accordance with the gradient in waterpotential from tip to base, could be demonstrated in translocation experiments with acid fuchsine dye and lead (EDTA) chelate. The occurrence of patches of vigorous growth within the continuum of a sand sedge plant system can be explained by the properties of the xylem translocation system of the plant.

Dormancy and germination ecology of two Harpagophytum species (Pedaliaceae) from an open Acacia savanna in Botswana were investigated. The maintenance of dormancy is governed partly by the seed coat but mainly by the endosperm and the embryo itself, as demonstrated by removal of the endosperm. Dissemination of the seed from the fruit can be delayed for several years without affecting the viability of the embryo, due to very low respiration rates.Germination can be enhanced slightly by high temperatures under natural conditions, and by gibberellic acid or removal of the endosperm under laboratory conditions. Relative growth rates for both Harpagophytum species are lower than for subtropical grasses and legumes, due to a strong investment in root and tuber biomass. Germination and seedling growth is discussed in relation to the drought avoidance syndrome and the animal disperser syndrome.

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