Fig. 5. Lily pollen proton flux measured in two concentrations of MES, pH 6.15.   A. Raw µV differences measured at positions marked by squares.   B. Computed diffusional flux and facilitated flux in 60 µM MES.   C. Computed diffusional flux and facilitated flux in 300 µM MES.  The probe is sensative to more global proton flux in the lower concentration MES.  Noise becomes a larger contributor to total flux in the higher concentration MES because the measureable information (µV difference over 10 µm excursion) becomes a smaller proportion of total proton flux.  The media used to examine the pollen tube growth contained 1.0 mM KCl, 0.05 mM CaCl₂, 1.6 mM H₃BO₃, x µM MES and 5% sucrose [1].