Spore

The word derives from the Greek spora, meaning "a sowing" or "a seed," from speirein, "to sow" or "to scatter" — the same root that gives "sporadic" (scattered at intervals), "diaspora" (a scattering of people), and the botanical term "sperm" through a different path. In classical Greek, spora was used for the act of sowing seed and for seed itself; the sense was of deliberate dispersal. The botanical term spore entered scientific Latin in the eighteenth century when botanists needed a word for the reproductive units of ferns, mosses, fungi, and algae — organisms that reproduced without seeds or flowers.

A spore is not a seed. A seed contains an embryo — a miniature plant with differentiated organs — together with stored food and a protective coat. A spore is typically a single cell, or a small group of cells, with no differentiated embryo and minimal stored reserves. What the spore carries is the genetic information and, often, a thick cell wall resistant to desiccation, heat, or chemical assault. Fern spores released in autumn may travel hundreds of miles on the wind before landing; bacterial spores (technically different but sharing the word) can survive conditions that would destroy any other form of life.

The fern's reproductive cycle involves two distinct plant generations — the alternation of generations that nineteenth-century botanists found so startling when they worked it out. The familiar fern frond is the sporophyte — the spore-producing generation — and on its underside, in the sori (clusters of sporangia), millions of spores are manufactured. Each spore germinates into a tiny, heart-shaped gametophyte — the sexual generation — which produces eggs and sperm. Only when a sperm fertilizes an egg does a new sporophyte fern begin to grow. The spore is not the beginning of the plant; it is the beginning of the sexual generation that precedes the plant.

Fungi produce spores in numbers that dwarf anything a flowering plant achieves. A single giant puffball can release seven trillion spores; a large bracket fungus may discharge billions per day during its fruiting season. Most of these spores land in conditions unsuitable for growth and simply die, but the scale of production ensures that a few find exactly the right substrate, humidity, and temperature. The spore's strategy is statistical: compensate for any single spore's low probability of success with an almost incomprehensible quantity of tries.