In the summer of 1981 sib plants, some shedding white pollen (c2/c2, whp/whp) and others shedding yellow pollen (C2/c2, whp/whp), were selfed. Forty-eight hours post-pollination, silks were cut from the ears and fixed in formalin-acetic acid-80% ethanol (1:1:8) for 24 hours at room temperature. The silks were transferred to 8M NaOH for 4 to 6 hours. The silks were dip-rinsed in water and examined under the light microscope without a coverslip. The basic condition clears the silk body and heightens flavonols.

The yellow pollen grains are seen as collapsed, empty shells still attached by their germination tubes to the silk body. Here and there traces of pollen tubes are visible, aligned with the vascular bundles.

Most of the white pollen grains are half empty, still anchored to the silk body. Germination tube progress is easy to discern, as the pollen cytoplasm is an off-brown color and filled with starch grains. Within the silk body, at a distance no more than twenty pollen grain diameters, are numerous, sizable, brown, grainy "bodies" with a ballooned appearance. This is not often seen on silks with yellow pollen.

Based also upon observations from the winter of 1980/81 using silks of maize x Tripsacum hybrids, which are more suited to live viewing, I offer this interpretation. A white pollen grain germinates, penetrates the silk, and grows a short distance, usually less than 10 pollen grain diameters. Suddenly, the tube bursts and the cytoplasm is forcibly extruded in a pulsating manner for a short time. The intra-silk "bodies" appear to be the accumulation of the contents of several burst tubes. The sterility is due to a "mass suicide" phenomenon, which involves 100% of the white pollen grains deposited on a silk.

These preliminary results were reported during the Symposium on Pollen Biology at the A.I.B.S. Meeting at Bloomington in June 1981.

Stephen A. Modena

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