Polygonum pollen. Coloured Scanning Electron Micrograph (SEM) of a pollen grain of the Knotweed Polygonum sp. The pollen grain is spherical. It has a highly sculptured outer wall (exine) of tiny columns (bacula), some fused at their tips to form ridges or walls (muri) arranged in a network. The ridges enclose irregular shaped areas studded with granular wart-like processes. The pollen grain, containing the male gametes, is dispersed, lands on the stigma of the flower and germinates. A tube grows out of the pollen grain, passes through the stigma and reaches the ovary. The male nuclei pass down the tube, fertilize the ovules and seeds are formed. Magnification: x1100 at 6x7 cm size. x1,750 at 4x5"~LANDSCAPE"