Spore

The term spore has several different meanings in biology. Spores are:

• diaspores (dispersal units) of fungi, mosses, ferns, fern allies, and a few other plants;
• The gametes of the higher vascular plants (angiosperms and gymnosperms)—the microspores (pollen) and megaspores (ovules) found in flowers and cones; these plants accomplish dispersal by means of seeds;
• resting stage in the life cycle of some bacteria and loosely applied to some animal resting stages.

Spores can be formed sexually or asexually, and therefore many different kinds of spores exist. In common parlance, the difference between "spore" and "gamete" is that a spore will germinate and develop into a thallus of some sort, whereas a gamete needs to combine with another gamete before developing further. However, the terms are somewhat interchangeable when referring to gametes, as indicated by the technical terminology given in the second definition above.

A chief difference between spores and seeds as dispersal units is that spores have very little stored food resources compared with seeds, and thus require more favorable conditions in order to successfully germinate. In their favor, spores are very hardy and require much less energy to produce. The strategy employed in producing spores, is to reach all the favorable locations by producing and dispersing very large numbers.

Diaspores

In the case of spore-shedding vascular plants such as ferns, wind distribution of very light spores provides great capacity for dispersal. Also, spores are less subject to animal predation than seeds because they contain almost no food reserve, however they are more subject to fungal and bacterial predation. Their chief advantage is that, of all forms of progeny, spores require the least energy and materials to produce.

Vascular plant spores are always haploid and vascular plants are either homosporous or heterosporous. Plants that are homosporous produce spores of the same size and type. Heterosporous plants, such as spikemosses, quillworts, and some aquatic ferns produce spores of two different sizes: the larger spore in effect functioning as a "female" spore and the smaller functioning as a "male".

Under high magnification, spores can be categorized as either monolete spores or trilete spores. In monolete spores, there is a single line on the spore indicating the axis on which the mother spore was split into four along a vertical axis. In trilete spores, all four spores share a common origin and are in contact with each other, so when they separate each spore shows three lines radiating from a center.