There was a statistically significant (P - 0.01) difference be- 
tween mean total chlorophyll concentrations of :chlorotic and 
apparently normal green sorghum plants. Chlorophyll concentrations 
in leaves were 9.4+1,5 (standard deviation) and 0.4+0.15 mg/g of 
plant tissue on a dry weight basis for normal and chlorotic plants, 
respectively. 
Chlorophyll concentrations of chlorotic and normal plants signifi- 
cantly (P - 0.01) affected reflectance measurements made in the 
field with a spectroradiometer (Fig. 3). Reflectance was 9.4, 
27.7, and 26.3 $ greater for chlorotic than for normal plant 
canopies at the 0.45-um (chlorophyll absorption band), 0.55-pm 
(green reflectance peak), and 0.65-um (chlorophyll absorption 
band) wavelenghts, respectively. These reflectances differences 
were caused by the unequal chlorophyll concentrations because 
chlorotic and normal plants had the same soil background, and 
their size and geometry were essentially the same. 
Band 5 (0.6 to 0.7 um) data were selected to represent the chloro- 
phyll absorption band at the 0.65-um wavelenght. Chlorotic sorghum 
areas 1.1 ha (2.8 acres) or larger were identified on a computer 
printout of band 5 data. This resolution was sufficient for prac- 
tical applications in detecting chlorotic areas in otherwise homo- 
geneous grain sorghum fields. 
Lead toxicity (Escobar, D.E. and H.W. Gausman, 1976) 
We conducted this study to ascertain if leaf reflectances of Mexi- 
can squash plants (Cucurbita pepo L., cv Tatume) grown with varied 
lead (Pb) concentrations differed enough for their possible use 
in spectrally detecting Pb-contaminated vegetation. 
The 500- and 1,500-ppm Pb treatments stunted the squash plants 
and caused them to be lighter green (less chlorophyll as will be 
shown later) than were the control plants. The 1,500-ppm Pb-treated 
plants did not have enough leaves for statistical comparisons 
with the other treatments. The average area per leaf for the 
500-ppm Pb treatment was significantly smaller (10.2 cm2) than 
that of the control and the 100-ppm Pb treatments (28.8 and 24.4 
cm“, respectively), which were not statistically different. Leaf 
thicknesses of 0.111, 0.110, and 0.112 mm, and water contents of 
91.2, 92.0, and 91.0% for the control, 100-, and 500-ppm Pb treat- 
ments, respectively, did not differ statistically. 
Plant Pb concentrations were 30, 87, 84, and 77 ppm for the control 
and 100-, 500-, and 1,500 ppm Pb treatments, respectively. The 
lower values for the 500- and 1,500-ppm Pb treatments, as com- 
pared with the 100 ppm Pb treatment, may have been caused by 
effects on Pb absorption because we observed root growth reduction. 
This agreed with plant growth reduction in sand culture (Miller 
and Koeppe, 1970) and seed germination inhibition (Dilling, 1926) 
with high Pb concentrations. The high Pb concentration of the 
control plants (30 ppm) may have been caused by atmospheric Pb 
pollution (Ganje and Page, 1972), because we conducted the experi- 
ment only 100 m from a heavily traveled highway. 
Reflectance spectra for the control and Pb-treatment squash leaves