spore

noun

(Gr. spora: seed) A propagative plant body consisting of a gametophyte enclosed in a non-cellular coat. Spores are enclosed within a capsule (sporangium) and are produced in groups of four (tetrads) when the parent cell divides meiotically. In more primitive plants the spores are identical (isospore) and the condition is called `homospory`. In more advanced, vascular plants spores of two sizes are produced and the condition is called `heterospory`. Small, male microspores are contained within a microsporangium; larger, female megaspores within megasporangia. Where spores occur in tetrads the contact surfaces produce a `trilete` mark on each of the four spores, marking the point for the germination of the prothallus. Less commonly, two contact surfaces are produced, resulting in a `monolete` marking. Spores which were probably produced singly are `alete`, with no obvious marking. Spores are produced by bacteria, algae, protozoa, fungi, and some plants. They are only just visible to the naked eye, but can be seen as clumps on the underside of fern leaves or under the cap of fungi. Unlike seeds, they contain only a few cells and no embryo, but still grow into new individuals. Most are liberated into the air and travel long distances in air currents, although most algae and some fungi have spores that can swim in water using beating hairs, or flagellae. Other kinds of spores lie dormant where they are produced; dormant spores of bacteria are the longest-surviving living material, resistant to extremes of temperature and drought. Those of the bacterium Bacillus anthracis, which causes anthrax, can survive up to 50 years.