Pollen-tube growth down the style is both positively and negatively chemotropic;the tube grows toward chemicals secreted by the pistil, and away from atmospheric oxygen.

• 花粉管沿着花柱的生长是既有正向性也有负向性的：花粉管向着由雌蕊分泌的化学物质生长，同时远离空气中的氧气生长。