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This paper describes the first monolithically integrated two-axis microtensile tester and its application to the automated stiffness measurement of single epidermal plant cells. The tensile tester consists of a two-axis electrostatic actuator with integrated capacitive position sensors and a two-axis capacitive microforce sensor. It is fabricated using a bulk silicon microfabrication process. The actuation range is +/-16 m along both axes with a position resolution of 20 nm. The force sensor is capable of measuring forces up to +/-60 N with a resolution down to 60 nN. The position-feedback sensors as well as the force sensor are calibrated by direct comparison with reference standards. A complete uncertainty analysis through the entire calibration chain based on the Monte Carlo method is presented. The functionality of the tensile tester is demonstrated by the automated stiffness measurement of the elongated cells in plant hairs (trichomes) as a function of their size. This enables a quantitative understanding and a model-based simulation of plant growth based on actual measurement data.