Color enhanced scanning electron microscope of a plum or gage pollen. Plum is a stone fruit tree in the genus Prunus, subgenus Prunus. European plums are the usually blue "prune-plums", seldom found in North American food stores. Italian plum trees are self pollinating (self-fertile). Image width: 80 micrometers. Magnification: 1,250x if the image is printed 10 cm wide.