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HCA cluster images of 40 pollen grains from two collection sites at (a) the Botanic Garden Jena of the Friedrich Schiller University Jena, and (b) the Forest Botanical Garden and Arboretum of the University of Göttingen. Five pollen samples from four different Betula species were recorded for each site. The five clusters describe the outer layers and inner core of each pollen grain, and correlate to the cluster spectra in Figure 2b.
