Ha. OK. This is interesting. Cucumber produces drops of dew along the serrated points of the leaf -- I'm not sure why -- excess moisture in the soil? Atmospheric pressure? Excess humidity/condensation?
Anyway, to me it looks like the beads of water formed and dried, and some kind of white powdery matter -- dust, pollen, talc.... salt? -- that had been trapped in the droplets had left those residue after the water evaporated.
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