An instrument containing a linear variable differential transformer was constructed to obtain continuous, nondestructive measurements of both short term changes in stem diameter and long term growth. In cotton plants, stem diameter, leaf water potential, and leaf relative water content are all closely related to net radiation at the top of the canopy. Leaves from the east and west sides of a plant show slight, but consistent differences in diurnal water potential patterns.Stem diameter and leaf water potential are not related by a single-valued function, since there is a diurnal hysteresis between the two, and growth causes an increase in diameter each night. However, the instrument can be used to monitor long term stem diameter growth.