Cotton plants grow by developing a series of nodes up the main stem. Branches begin to form after the fifth or sixth node, allowing for the formation of the cotton square.
A square is part of the developing cotton fruit -- along with the bloom and boll -- on the branch of a cotton plant. "Squares are the flower bud that first appears on the plant when reproductive growth begins. Squares grow for about three weeks before a bloom appears," writes the University of Missouri Extension Service.
The square period of this growth culminates with a bud, followed by blooming as the square morphs into a flower, eventually transforming into a boll, the rounded sac of seeds that contains the characteristic fibers of the cotton plant. Squares work their way up the fruiting branches of the plant one after another.
A successful crop will see multiple squares on each branch. "A 'pinhead' square is the first stage at which the square can be identified. The next stage of square growth is 'match-head' or 'one-third grown' square," reports the Cooperative Extension System, a U.S. partnership of 74 universities. The final stage is referred to as "squaring."