POLLEN GERMINATION AND POLLEN-TUBE GROWTH IN THE MARINE ANGIOSPERM, ZOSTERA-MARINA L

The marine angiosperms have adapted to a hydrophilous pollination mode, in which pollen is released and captured underwater. There has been some misunderstanding as to the fate of pollen following capture on stigmas. To address this question, naturally shed pollen grains were transferred to stigmas of carpellate flowers of Zostera marina L. (eelgrass). These pollinated carpels were stained for callose, using aniline blue and examined under epifluorescence microscopy. Pollen germination, which occurred 2 h after pollination, first appeared as protuberances on the pollen (the so-called 'beaded pollen'). Once the tubes penetrated the stigma they grew straight through to the stylar canal and into the locule. At the funiculus of the uniovulate ovary, the pollen tube paths diverged and became disorganized as the tubes grew in many directions around the ovule towards the rear of the locule. Pollen tubes then grew towards the micropyle, and continued directly into the egg apparatus, where fluorescence was observed, indicating fertilization.