Cinnamon tree pollen. Scanning electron micrograph of pollen of the Cinnamon tree Drimys winteri. The pollen is found in associations of 4 grains, known as tetrads. The grains are not pressed together closely in the tetrad. The outer wall (exine) of the grain comprises rod-like processes (bacula), fused at their tips, forming a network of ridges (muri) and surrounding a circular germinal pore. When the pollen, containing male gametes, lands on the stigma of a flower, it germinates. A pollen tube grows out of a pore, down the stigma, to the ovary. Male nuclei pass down the tube and fertilize the ovules to form seeds. Magnification: x2275 at 10x8 inch size.