Chlorophyll content meter
Leaf greenness was determined with a prototype of the Opti-
Sciences CCM-200 chlorophyll content meter (Opti-Sciences,
Tyngsboro, MA). This instrument uses differential transmission
at two wavelengths, 940 and 665 nm, to determine the
absorbance of chlorophyll pigments (whereas the current production
model uses a 655 nm absorbance beam). Beam energy
is sampled pre- and post-transmission, and the 940 nm reference
beam is standardized according to the manufacturer’s
instructions. The ratio of the red absorbance beam to the standardized
infrared reference beam gives the chlorophyll
content index (CCI).