Ten randomly selected peanut plants (cv. NC 7) were harvested from the Central Crops Research Station, Clayton, North Carolina. Peanut pods were opened, and twenty seeds were classified into early and late developmental stages according to criteria modified from Pattee et al., (1974). The peanut seeds were ranked developmentally based on interior pericarp surfaces, testa characteristics, and seed size and shape. Peanut seeds were classified as being in an early developmental stage (stages 6 -7) according to the following criteria: (1) pods with light-colored interior pericarp surfaces, (2) testa with longitudinal wrinkles, and (3) seeds approximately 8 mm in length and having a length/width ratio average of 2.2. Peanut seeds were classified as being in a late developmental stage (stages 12 to 13) according to the following criteria: (1) pods with dark-colored interior pericarp surfaces, (2) smooth testa, and (3) seeds approximately 20 mm in length and having a length/width ratio average of 1.6.

Testa was carefully removed from seeds with a razor blade. The individual seeds were separated into the two cotyledons that comprise each seed. Tissue blocks (1 mm³) of mid-region cotyledon were cut with a razor blade and fixed in Karnovsky's fixative (Karnovsky, 1965) as modified by Young and Schadel (1989). The modified fixative was prepared by mixing 25 mL of 8% formaldehyde, 3.6 mL of 70% glutaraldehyde and 28.6 mL of 0.l M sodium phosphate buffer. The tissue blocks were fixed under vacuum for 30 min at 23 C and then fixed at atmospheric pressure for 48 hr at 4 C. Following six changes of 0.1 M sodium phosphate buffer (4 C, pH 7.0), the material was post-fixed for l hr in l% osmium tetroxide in 0.1 M buffer (4 C, pH 7.0) and dehydrated at room temperature at 15 min intervals in a graded series of aqueous ethanol (10, 25, 50, 75 and 95%) and then finally at two 30 min intervals in absolute ethanol.

Dehydrated tissue for scanning electron microscopy was critical point dried in a Tousimis unit (Ladd Research, Williston, VT) using liquid carbon dioxide. Dried sections were mounted on aluminium specimen stubs with double-sided tape and silver conducting paint. Tissue blocks on stubs were coated with 30 nm of gold-palladium alloy with a Hummer V sputter-coater fitted with a Technics digital thickness monitor. Specimens were viewed with a Phillips 505T SEM at a working distance of 15 mm and an accelerating voltage of 15 kV.

Dehydrated tissue for transmission electron microscopy was also embedded in Spurr's resin for long pot-life (Spurr, 1969). Ultrathin sections cut with a Reichert ultramicrotome were stained with 4.0% uranyl acetate for 45 min, followed by 0.4% lead citrate for 4 min. Sections were examined with a JEOL 100S transmission electron microscope.

Peanut cotyledonary cell starch granules were observed to originate and grow in amyloplasts (Fig. 1). The amyloplast consists of a double membrane enclosing a ground substance, the stroma, in which the electron translucent starch granule develops. Electron dense material believed to be enzyme complexes were observed within the stroma (Fig. 2). Fully developed as well as developing starch granules were observed during early stages of seed development (Fig. 3). Simple starch granules (single granule per amyloplast) as well as compound starch granules (more than one granule per amyloplast) were noted (Fig. 4). The potential for increase in size of starch granules was observed to result from the deposition of starch material on the surface of pre-existing granules (Fig. 5). The compound granules in which the granuli remained distinct and separate showed no evidence of such aggregation (Fig. 6).

Due to the similar spherical nature of protein bodies and simple starch granules, SEM was capable of distinguishing only the compound starch granules (Fig. 7) in peanut cotyledonary cells.