XET activity was shown to be present in all major groups of green plants. These data suggest that an XET-related growth mechanism originated before the evolutionary divergence of the Chlorobionta and open new insights in the evolution of the mechanisms of primary cell wall expansion.

The results are presented of a detailed plant macrofossil analysis of a 14C dated Holocene organic sequence from a sub-Antarctic island, South Georgia. In the peat infilling of a rock basin 31 bryophyte species and many of the principal species of the present-day angiosperm flora, associated with bog communities, have been identified. The zonation of the bryophytes and the seeds and fruits shows a striking correspondence with the sediment stratigraphy, and indicates five ecological phases. The first four reflect a succession from a minerotrophic shallow pool to an ombrotrophic Warnstorfia-Polytrichum bog. After the deposition of a greyish-brown layer, c. 2200 "4C years BP, a wet Deschampsia-Warnstorfia-SanioniaRostkovia bog came into existence, which is still present today. The ecological phases are radiocarbon dated. They can be interpreted in terms of climate development during the Holocene. Climate ameliorated rapidly at about 10 000 14C years BP followed by a drier period. Around 7000 '4C years BP the climate became wetter and the following c. 2500years probably represent the climatic optimum. Between 4500 and 2600 '4C years BP, drier conditions prevailed at the study site. The most striking change occurred at 2600 14C years BP when a marked change in vegetation and ecology indicates much wetter conditions.

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Analyses of pollen, plant macrofossils (seeds, fruits, wood and mosses), molluscs, diatoms and vertebrate (mainly fish) remains allowed a detailed reconstruction of a middle-Holocene alluvial forest and its associated hydrological conditions. The use of multiple proxies resulted in a taxonomically more detailed and environmentally more comprehensive understanding of terrestrial as well as aquatic habitats. The results demonstrate possible biases in palaeoecological reconstructions of alluvial and estuarine environments drawn from single proxies. Many locally occurring woody taxa were underrepresented or remained undetected by pollen analyses. Seeds and fruits also proved to be inadequate to detect several locally important taxa, such as Ulmus and Hedera helix. Apparently brackish conditions inferred from diatoms, pollen and other microfossils conflicted strikingly with the evidence from molluscs, fish bones and botanical macroremains which suggest a freshwater environment. Brackish sediment (and the microfossil indicators) is likely to have been deposited during spring tides or storm surges, when estuarine waters penetrated more inland than usual. Despite the reworking and deposition of estuarine and saltmarsh sediment well above the tidal node at such events, local salinity levels largely remained unaffected.

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