Hydration of pollen grains and growth of pollen
tubes on stigmas. A to D, Pollen on stigma papillae projecting through
the exudate into air at the RH prevailing in the laboratory. Dry pollen
(A and B) and pollen presoaked in exudate and drained (C and D) did not
hydrate. Photographs were taken 1 h (A and C) and 18 h (B and
D) after pollination. E and F, Pollen on stigma flooded with mineral
oil at the start of the experiment and photographed 30 min and 4 h
after pollination did hydrate. G and H, Growth of pollen tubes on
stigmas held at controlled RH, photographed 16 h after
pollination. G, Stigma at 88% RH. Only stigma papillae are visible
above the exudate. H, Stigma at 100% RH. Pollen tubes have grown from
the stigma into the surrounding air. pap, Papillar cell; pg, pollen
grain; pt, pollen tube. Scale bar in A = 50 μm and refers to A
through F; scale bar in G = 50 μm and refers to G and H.