Abstract: Atomic Force Microscopy in force modulation mode was used to study the elastic properties of the different fibre wall layers of the tension wood of holm oak and normal wood of boco. The method is based on the measurement of the resonance frequency of the microscope lever in contact with the sample. This frequency is related to the reduced Young modulus E* = E/(1-nu(2)) of the material, supposed to be isotropic. 'Elastic' images of the cell are obtained simultaneously with the topographic images, which allows the observation of the mechanical properties of the cells at a nanometric scale. Layers G, S-1, S-2 and ML can clearly be distinguished. By comparison with known materials an estimation of the absolute modulus is given in the range 5-20 GPa, but should be considered with caution, because the inherent anisotropy of the materials has not been taken into account.

Abstract: Cecropia (Cecropiaceae) is a Neotropical genus of pioneer plants. A review of bat/plant dispersal interactions revealed that 15 species of Cecropia are consumed by 32 species of bats. In French Guiana, bats were captured in primary and secondary forests, yielding 936 fecal samples with diaspores, among which 162 contained fruits of C. obtusa, C. palmata, and C. sciadophylla. A comparative morphological and anatomical study of fruits and seeds taken directly from herbarium specimens, bat feces, and an experimental soil seed bank was made. Contrary to previous reports, the dispersal unit of Cecropia is the fruit not the seed. Bats consume the infructescence, digest pulp derived from the enlarged, fleshy perianth, and defecate the fruits. The mucilaginous pericarp of Cecropia is described. The external mucilage production of Cecropia may facilitate endozoochory. The exocarp and part of the mesocarp may be lost after passage through the digestive tract of bats, but fruits buried for a year in the soil seed bank remain structurally unchanged. Fruit characters were found to be useful for identifying species of bat-dispersed Cecropia. Bat dispersal is not necessary for seed germination but it increases seed survival and subsequent germination. Fruit structure plays a significant role in seed longevity.

Abstract: A range of mechanical and physical properties were determined for 96 specimens of chestnut wood and for wood types ranging from compression to tension wood; tests included (1) growth stress, (2) longitudinal Young's modulus in green and air-dried states (3) shrinkage in longitudinal and tangential directions. Anatomical observations permitted determination of the proportion of fibres with a gelatinous layer. The influence of these atypical fibres on macroscopic wood properties is examined and discussed. A basic model is proposed to determine their properties in theoretically isolated conditions.

Abstract: Oak chloroplast DNA (cpDNA) variation was studied in a grid-based inventory in western Central Europe, including Belgium, The Netherlands, Luxembourg, Germany, the Czech Republic, and the northern parts of Upper and Lower Austria. A total of 2155 trees representing 426 populations of Quercus robur L. and Q. petraea (Matt.) Liebl. were screened for polymorphism in up to four PCR-amplified cpDNA fragments. Eleven haplotypes belonging to four lineages were detected; these lineages were formerly restricted to glacial refugia in the Iberian Peninsula, the Apennine Peninsula and the Balkan Peninsula. The haplotypes originating from the Apennines are particularly well represented in the study region, but there is also a significant contribution from the other refugia, which explain the high overall level of cpDNA diversity. The strong human impact in western Central Europe during the past centuries, which has resulted in the clearance of most forests, was followed by reforestation, sometimes involving seed transfers. Despite this strong human impact, broad geographic patterns of lineages and haplotypes could still be detected. To evaluate further the consequences of the former human activities on the present day oak cpDNA genetic structure, four regions where increasingly strong human impact was anticipated (ranging from hilly regions in southern Germany to roadsides plantations in The Netherlands) were selected. There, a comparison of the levels of intrapopulation cpDNA diversity and spatial structuring was made. Over the whole area, within stand diversity was significantly higher in Q. robur than in Q. petraea (h(S) = 0.24 vs. 0.16). Since total diversity is identical for both species, this results in a significantly lower level of fixation for Q. robur than for Q. petraea (G(ST) = 0.68 vs. 0.79). The analyses also reveal a decrease of fixation with increasing human impact on oak populations. The Dutch roadside plantations (Q. robur) exhibit a very low level of fixation (G(ST) = 0.28) as compared to Q. petraea in southern Germany (G(ST) = 0.91). The significance of the spatial genetic structure was tested using geostatistical methods. For the complete data set, a strong spatial genetic structure is confirmed, with higher than average genetic similarities between populations distant from up to 270 km, whereas there is no spatial structure in the roadside plantations in The Netherlands or in the northern German lowlands. These results should help to differentiate introduced from autochthonous populations, and provide a framework for the identification of the geographic origin of seed lots. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We describe five new species in the aurita group of the genus Azteca: Azteca andreae sp. n. (French Guiana), Azteca diabolica sp. n. (Panama), Azteca laurae sp. n. (Brazil), Azteca linamariae sp. n. (Brazil and Colombia) and Azteca snellingi sp. n. (Panama). Four of these new species are based on gynes, while the last is based only on the worker caste. All of them bear the aurita group characteristics. The second taxon is remarkable, as it differs from all of the other members of the group in the exaggerated, horn-like extensions of the posterolateral vertex margins. Azteca snellingi sp. n. is named in honor of our colleague, Roy Snelling, in tribute to his life-long contribution to knowledge of the world of Hymenoptera. A key to all known species of the aurita group, based on gynes, is provided. We report also for the first time an intercast case for the genus Azteca, based on an Azteca schimperi specimen.