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 st igmas. To address this question, naturally shed pollen grains were tra nsferred to stigmas of carpellate flowers of Zostera marina L. (eelgra ss). 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 protuberance s on the pollen (the so-called 'beaded pollen'). Once the tubes penetr ated the stigma they grew straight through to the stylar canal and int o the locule. At the funiculus of the uniovulate ovary, the pollen tub e paths diverged and became disorganized as the tubes grew in many dir ections around the ovule towards the rear of the locule. Pollen tubes then grew towards the micropyle, and continued directly into the egg a pparatus, where fluorescence was observed, indicating fertilization.