Pollen cells. Sperm cells of Pinophyta and Gnetophyta are without flagella, and are carried by the pollen tube, while those of Cycadophyta and Ginkgophyta have many flagella. When placed on the stigma of a flowering plant, under favorable circumstances, a pollen grain puts forth a pollen tube, which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the micropyle of an ovule. The nucleus of the tube cell has meanwhile passed into the tube, as does also the generative nucleus, which divides (if it hasn't already) to
Annulus (botany) dissolve to allow the cap to fall off and the spores to be released. Annulus (botany) An annulus in botany is an arc or a ring of specialized cells on the sporangium. These cells are arranged in a single row, and are associated with the release or dispersal of spores. In leptosporangiate ferns, the annulus located on the outer rim of the sporangium and serves in spore dispersal. It consists typically of a ring or belt of dead water-filled cells with differentially thickened cell walls that stretches about two-thirds around each sporangium in leptosporangiate ferns. The thinner walls on the