Sensor apparatus for measuring transpiration of a plant specimen (P), comprising: a printed circuit board device ; a first moisture sensor for sensing a first air humidity in the region of the plant specimen (P), said first moisture sensor being arranged and contacted on the printed circuit board device ; a second moisture sensor for sensing an ambient air humidity, said second moisture sensor being arranged and contacted on the printed circuit board device ; a first chamber bounding structure for bearing against the plant specimen (P), wherein the first chamber bounding structure projects relative to the printed circuit board device and frames the first moisture sensor in such a way that when the chamber bounding structure bears against the plant specimen (P), the first moisture sensor is arranged in an enclosed first air chamber bounded by the plant specimen (P) and the first chamber bounding structure , wherein the printed circuit board device or the first chamber bounding structure has a first ventilation opening , which connects the first air chamber to the surrounding environment (U) in a fluidically conducting manner; a second chamber bounding structure , which together with the printed circuit board device forms an enclosed second air chamber , in which the second moisture sensor is accommodated, wherein the printed circuit board device or the second chamber bounding structure has a second ventilation opening , which connects the second air chamber to the surrounding environment (U) in a fluidically conducting manner; and a securing device for securing the plant specimen (P) to the first chamber bounding structure . a printed circuit board device ; a first moisture sensor for sensing a first air humidity in the region of the plant specimen (P), said first moisture sensor being arranged and contacted on the printed circuit board device ; a second moisture sensor for sensing an ambient air humidity, said second moisture sensor being arranged and contacted on the printed circuit board device ; a first chamber bounding structure for bearing against the plant specimen (P), wherein the first chamber bounding structure projects relative to the printed circuit board device and frames the first moisture sensor in such a way that when the chamber bounding structure bears against the plant specimen (P), the first moisture sensor is arranged in an enclosed first air chamber bounded by the plant specimen (P) and the first chamber bounding structure , wherein the printed circuit board device or the first chamber bounding structure has a first ventilation opening , which connects the first air chamber to the surrounding environment (U) in a fluidically conducting manner; a second chamber bounding structure , which together with the printed circuit board device forms an enclosed second air chamber , in which the second moisture sensor is accommodated, wherein the printed circuit board device or the second chamber bounding structure has a second ventilation opening , which connects the second air chamber to the surrounding environment (U) in a fluidically conducting manner; and a securing device for securing the plant specimen (P) to the first chamber bounding structure . <EOS>