SPORE

a reproductive cell capable of developing into a new individual without fusion with another reproductive cell. Spores thus differ from gametes, which are reproductive cells that must fuse in pairs in order to give rise to a new individual. Spores are agents of asexual reproduction, whereas gametes are agents of sexual reproduction. Spores are produced by bacteria, fungi, and green plants. Bacterial spores serve largely as a resting, or dormant, stage in the bacterial life cycle, serving to preserve the bacterium through periods of unfavourable conditions. Many bacterial spores are highly durable and can germinate even after years of dormancy. Among the fungi, spores serve a function analogous to that of seeds. Produced and released by specialized fruiting bodies, such as the edible portion of the familiar mushrooms, fungal spores germinate and grow into new individuals under suitable conditions of moisture, temperature, and food availability. Among green plantsall of which have a life cycle characterized by alternating generations of asexually and sexually reproducing individualsspores are the reproductive agents of the asexual generation. Produced by the sporophyte (i.e., spore-bearing) generation, plant spores give rise to the gametophyte (i.e., gamete-bearing) generation. Spores are most conspicuous in the non-seed-bearing plants, including algae, liverworts, mosses, and ferns. In these lower green plants, as in fungi, the spores function much like seeds. In general, the parent plant sheds the spores locally; the spore-generating organs are frequently located on the undersides of leaves. The spores of plants that inhabit the edges of bogs or lakes are frequently shed into the water or are carried there by rain and are preserved in the sediments. Wind dispersal is a factor in plants that shed their spores explosively. Among the seed-bearing plantsthe gymnosperms and the angiospermsthe spores are far less conspicuous. They are not released from the parent plant, but rather they germinate into microscopic gametophyte individuals that are entirely dependent upon the sporophyte plant. Gymnosperms and angiosperms form two kinds of spores: microspores, which give rise to male gametophytes, and megaspores, which produce female gametophytes.