An Automatic System for Measuring Shoot Length in Sitka Spruce and Other Plant Species

Abstract

A device was designed to measure the shoot length of Sitka spruce (Picea sitchensis) in order to study the influence of the physical environment on the plant. The device minimizes physical contact with the shoot apex. An electric motor is used to periodically reposition a light transmitter-receiver system and an associated multiturn potentiometer so that the light beam is just clear of the shoot tip. Tests show that the device has a resolution of .+-. 0.1 mm at constant temperature and .+-. 0.2 mm over the range 10-40.degree. C. It can record a maximum change in shoot length of 250 mm without remounting. The principle can be applied to measurement of other plant species. Measurements obtained by the device show diurnal variations in the growth rate of the leading shoot of a 13-yr old Sitka spruce tree.