= 722 = 
tance attachment, was used to measure total diffuse reflectance on 
upper (adaxial) surfaces of single leaves over the 6,5- to 2.5-un 
waveband. Data were corrected for decay of the barium sulfate stan- 
dard (Allen and Richardson, 1971) to give absolute radiometric 
data. Laboratory measurements of leaf reflectance and fixations 
of tissue were completed within about 6 h after leaves were collec- 
ted. Leaf thickness was measured with a linear-displacement trans- 
ducer and digital voltmeter (Heilman et al., 1968). Leaf area was 
determined with a planimeter. Water content of leaves was deter- 
mined on a dry-weight basis; leaves were oven-dried at 68C for 72 h 
and cooled in a desiccator before weighing. Total chlorophyll was 
determined by a routine method (Horwitz, 1965) on leaf samples 
stored at -15C€* 5 C. 
Tissue pieces sampled from the center of leaves were fixed in for- 
malin-acetic acid-alcohol, dehydrated with a tertiary butanol 
series, embedded in paraffin, stained with the safranin fast-green 
combination, and transversally microtomed at 12-um thickness 
(Jensen, 1962). Photomicrographs were obtained with a Zeiss Stan- 
dard Universal Photomicroscope. 
To reduce the enormous amount of spectrophotometrically generated 
data and facilitate interpretation, seven wavelengths, were selected 
£rom the 41 wavelengths measured at o,o5-um increments over the 
o.50-to 2.50 - um waveband. Wavelengths selected were 0,55, o.65, 
0,85,1.45,1.65, 1.95, and 2.20 um; representing, respectively, the 
green reflectance peak, chlorophyll absorption band, a wavelength 
on tke near-infrared plateau, the 1.45-um water-absorption band, 
the 1.65-um water-absorption band, the 1.95-um water-absorption 
band, and the 2.2-um peak. 
An Exotech Model 20 spectroradiometer (Leamer et al., 1973) was 
used to measure reflected radiation from nonstressed and stressed 
single plant canopies over the o.5-to 2.5-um waveband. Measurements 
were usually made with sensors with a 15-degree field of view 
(0.2 m^) placed 1.5 m above each plant canopy. 
Standard statistical techniques were used (Steel and Torrie, 1960) 
and Duncan's multiple range test (Duncan, 1955) was usually used 
to test differences among means. Randomized complete block experi- 
ments were generally used. At least 1o leaves were randomly collec- 
ted from each treatment for laboratory relfectance measurements on 
singe leaves; field measurements were replicated five times. 
Results and Discussion Stressed vs nonstressed 
Nematodes on cotton (Gausman et al., 1975 a) 
We conducted this research to determine if there were differences 
between the light reflectance for leaves of cotton (Gossypium hirsu- 
tum L.) plants grown with a low- or no-nematode population (non- 
stressed) and plant leaves grown with a high nematode population 
(stressed). 
Stressed cotton plants were stunted with fewer, smaller, and darker- 
green leaves than nonstressed plants. Differences between non- 
stressed and stressed plants in leaf water content and leaf area 
were highly significant (P = 0.01). Nonstressed leaves were larger 
in area (25.5 cm“) than stressed leaves (17.3 cm ) with lower wa- 
ter contents (77.5%) than stressed leaves (78.3%). Leaf thicknesses 
of nonstressed (.16 mm) and stressed (.15 mm) leaves were statis- 
tically alike.