Cotton germination begins as the seed absorbs water and oxygen through its chalaza after planting. The water swells the dormant tissues, and cell growth and division begin to take place. The radicle emerges through the micropyle, turns downward, and grows deeper into the soil, providing a taproot that will supply water and nutrients throughout the life of the plant. The hypocotyl elongates from the radicle and forms an arch or crook that begins to push up through the soil, a brief period often referred to as the “crook stage”.

Cotton seedling emergence normally takes place 4 to 14 days after planting. At the soil surface, the hypocotyl straightens and pulls the folded cotyledons out of the soil, a process known as epigeal germination. After the cotyledons are pulled through the soil surface, they unfold and expose the epicotyl and the apical meristem, or growing point, which will be the source of subsequent growth. At this point, germination and seedling emergence are complete and the plant begins its active vegetative growth.

Figure 1. Germination and early seedling development. Root growth dominates the early growth of the plant.

The Cotyledons and First True Leaves

The cotyledons serve a dual role in cotton germination. Before they unfold, they supply stored food to the germinating seedling. After the cotyledons unfold, they produce chlorophyll, become green, and produce energy through photosynthesis. The apical meristem emerges at the base of the cotyledons, and all further vegetative and reproductive growth of the plant occurs through the meristems.

Figure 2. The cotyledons are storage organs that are formed in the seed and emerge from the soil as leaf-like structures oriented opposite each other on the seedling stem. The cotyledons provide nutrients for the seedling. The apical meristem emerges through the cotyledons and will be the source of new growth as the plant matures.

A week or so after seedling establishment, the first true leaf appears above the cotyledons. The first leaf shifts the plant’s primary energy source from storage to photosynthesis and signals the move from emergence to vegetative growth.

Figure 3. The first true leaf emerges about 7 days after seedling establishment. From this point on, the meristems will produce all vegetative and reproductive structures on the plant.