1) Measuring instrument 
An auxanometer (Gr. auxain, `to grow` + metron, `measure`) is an apparatus for measuring increase or rate of growth in plants. In case of an arc-auxanometer (see picture), there is a wire fixed with the plant apex on one end and a dead-weight on the other. It passes over a pulley which has a pointer attached to it. When the plant`s height inc...
instrument for measuring growth of plants
• (n.) An instrument to measure the growth of plants.
Aux`a·nom'e·ter noun [ Greek ... to cause to increase + -meter .] An instrument to measure the growth of plants. Goodale.