950 
Fig. 3 Fluorescence images of the lower side of a leaf of the green form of Nicotiana tabacum L. su/su. The brighter 
parts represent leaf areas with a higher fluorescence. A. Distribution of the blue fluorescence F440 mainly in the leaf 
veins, and B. of the red chlorophyll fluorescence F690 in the intercostal fields between the leaf-veins. 
Fig. 4 Image of the fluorescence ratio blue/red 
(F440/F690) of the lower leaf-side of an aurea 
tobacco leaf. The numbers indicated represent the 
ratio which is higher in the main leaf-vein (0.70 and 
0.60) than in the intercostal fields (0.19 and 0.24).