Stem Elongation & Heading
Stem elongation, or jointing, occurs when stem internodes increase in length and bring the nodes above ground. The uppermost five or six internodes elongate, begin- ning with the lowest of these. The appearance of the first node above ground marks the beginning of jointing. Jointing begins about the time all spikelet primordia have formed. The flowering structure (inflorescence) of wheat, triticale, and barley is called a spike; that of oat is called a panicle. Inflorescences are composed of spikelets, each consisting of one or more flowers, called florets, at nodes along the spike or panicle. In barley, three spikelets form at each node, and each spikelet has a single floret. All three spikelets are fertile in 6-row barley; only the middle spikelet is fertile in 2-row barley. One spikelet forms at each node of the wheat and triticale spike, but each spikelet consists of three to six potentially fertile florets. In the highly branched panicle of oat, individual spikelets form at the end of branches.
During stem elongation the spike or panicle increases in length from about 0.1 inch (3 mm) to its final size, and individual florets mature. All stages of spikelet develop- ment in wheat, triticale, and barley begin near the middle of the spike and proceed toward the base and tip. Development of oat florets begins at the tip of the panicle branches and proceeds toward the base. The last leaf of the small grain plant to emerge is called the flag leaf. When the flag leaf blade has completely emerged, the appearance of its ligule (a short membrane on the inside of the leaf at the junction of the blade and sheath) marks the beginning of the boot stage. During boot stage the enlarging spike swells and splits the sheath of the flag leaf. Heading begins when the spike begins emerging through the flag leaf collar and is complete when the base of the spike is visible.