STUDIES ON THE DETECTION OF LETTUCE MATURITY: ANATOMICAL OBSERVATIONS AND REFLECTANCE MEASUREMENTS IN THE VISIBLE RANGE (350–650 nm)

Abstract

Reflectance in the visible (350–650 nm) range has been measured through the 1977 growing season on four cultivars of head lettuce. The transmittance of the light reflected by the lettuce head for all cultivars at all stages of development exhibited a maximum value at 555 nm which corresponds exactly to that of chlorophylls. This is an indication that chlorophylls are the main contributors to leaf reflectance. The amplitude of the 555-nm peak varied with the degree of maturity; however, it was not directly proportional to the chlorophyll concentration of leaf tissues. The pattern of these variations was related with the morphological and anatomical changes that occurred in the head leaf.