Auxospores and frustules from each of the cultures were subjected to SEM examination on flat polycarbonate filter as in [36 ] or a grooved LP substrate as in [37 ], as appropriate. Specimens were examined using a JEOL JSM-5600 SEM (JEOL USA, Peabody, MA, USA) at the Digital Microscopy Facility, Mount Allison University, operating at 10 kV and 8–20 mm working distance. Diameters of cells in auxosporulating cultures were measured using dmfMeasure software [38 ]. A complete metric data set for the clones is available in [32 (link)]. Valve structure terminology followed [33 ] and [39 ] while the structures associated with auxosporulation were named following [7 ].
EDS was performed with the same instrument equipped with an Oxford Inca Energy 200 EDS system and at 20 mm working distance. Since the only element of interest in this study was silicon (Si-Kα, X-ray energy 1.74 keV), an accelerating voltage of 10 keV provided sufficient overvoltage for efficient X-ray excitation. Spectra were acquired for 100 s (dead time corrected) at 0.1 nA beam current, energy range 0–10 keV into 1024 channels. The EDS spectra were collected from intact and unobstructed structures and/or auxospores. Spectra from the polycarbonate support filter adjacent to the auxospores were also routinely taken and showed no remote excitation from neighboring siliceous components (if present) at distances as close as 3 μm.
EDS was performed with the same instrument equipped with an Oxford Inca Energy 200 EDS system and at 20 mm working distance. Since the only element of interest in this study was silicon (Si-Kα, X-ray energy 1.74 keV), an accelerating voltage of 10 keV provided sufficient overvoltage for efficient X-ray excitation. Spectra were acquired for 100 s (dead time corrected) at 0.1 nA beam current, energy range 0–10 keV into 1024 channels. The EDS spectra were collected from intact and unobstructed structures and/or auxospores. Spectra from the polycarbonate support filter adjacent to the auxospores were also routinely taken and showed no remote excitation from neighboring siliceous components (if present) at distances as close as 3 μm.
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