FIGURE 3—SRXTM images of the megaspore Arcellites sp. (S171531) from the Early Cretaceous Torres Vedras locality, Portugal; dataset acquired using a 203 objective and 20 lm thick LAG:Ce scintillator (voxel size 0.37) at 10 keV (1) and a 403 objective with a 5.9 lm thick LSO:Tb scintillator (voxel size 0.1625) at 10 keV (2–6); images in 1, 2 and 4, 5 have been reconstructed uniquely exploiting absorption contrast and pure edge-enhancement. Images in 3, 6 were obtained using simple phase retrieval (Paganin et al., 2002), but with the subsequent addition of the high frequency component of the original data to minimize loss in spatial resolution inherent in phase retrieval. 1–3, 2-D reconstructions of a transverse section through the body of the megaspore showing wall ultrastructure composed of a thin inner, almost solid, uniform layer, a middle granular-fibrous layer of uneven thickness, and an outer layer penetrated by very fine canals; note difference in resolution between 1 originating from a tomographic volume obtained with a 203objective and a 20 lm thick LAG:Ce screen, and
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