THE EFFECTS OF BEARING ON THE ULTRASTRUCTURE OF STIGMAS AND STYLES OF COX'S ORANGE PIPPIN FLOWERS

Twenty Cox's Orange Pippin trees on Malling 9 rootstock were selected for uniformity, and at petal-fall 10 were completely defruited. The remaining trees carried a heavy crop. The development of flowers was monitored and the effect of bearing was observed on flower number and size.

At anthesis flowers were collected for electron microscopic examination of stigmatic and stylar tissue. Styles were cut at the base and placed immediately in cold 2.5% glutaraldehyde buffered to pH7–7.3.

After fixation for 24 hours tissue for transmission electron microscopic examination was further dissected, washed in cacodylate buffer and post fixed in 1% osmium tetroxide buffered to pH7–7.3 before dehydration and embedding in epoxy resin. Thin sections were cut using an LKB ultra-microtome and examined with an AEI Corinth transmission electron microscope. For better contrast, by differential electron scattering of cell components, sections were double stained in uranyl acetate and lead citrate.

For scanning electron microscopy tissue was dehydrated and critical point dried in CO₂. The stigma and style were then gold coated and examined with a Jeol JSM 35.