Figure 2.

Hydration, germination, and directional growth of pollen tubes in exudate or olive oil close to an interface with an aqueous medium. A to C, Progressive hydration and germination of pollen grains in exudate 50 min, 3 h, and 4.5 h, respectively, after injection of the aqueous medium. Pollen grains closest to the interface hydrated and germinated first. The pollen tube emerged from the aperture closest to the interface and grew toward the aqueous medium. D and E, Growth of two tubes in exudate toward the interface 5 h after the injection of aqueous medium. The direction of pollen tube growth was determined by both the position of the germinal aperture and the axis of polarity of the tip (photographed 5 h after establishment of the interface). F, Pollen in exudate between two interfaces with aqueous medium showing growth of tubes toward the nearest interface (photographed after 6 h). G and H, Pollen in olive oil 5 min and 5 h, respectively, after injection of aqueous medium. Pollen spanning the interface germinated first and tubes emerged into the aqueous medium. I, Pollen in an emulsion of aqueous medium in olive oil close to a boundary with a predominantly aqueous phase. The pollen tube did not grow toward the boundary (photographed after 5 h). aq, Aqueous medium; aq, predominantly aqueous phase; ex, stigma exudate; oil, predominantly oil phase; pg, pollen grain; pt, pollen tube. Arrowheads indicate apertures in pollen grain; lines indicate extended short axes of pollen grains based on photographs of partially hydrated grains. Bar in H = 50 μm and refers to the entire figure.