The culm, or jointed stem of the rice, is made up of a series of nodes and internodes.
Fig. 11 - Culm, nodes, and internodes.
Young internodes are smooth and solid. Mature internodes are hollow and finely grooved with a smooth outer surface. Generally, internodes increase in length from the lower to the upper portions of the plant. The lower internodes at the plant base are short and thick.
Fig. 12 - Young and mature internodes.
The node is the solid portion of the culm. The node or nodal region bears a leaf and a bud. The bud is attached to the upper portion of the node and is enclosed by the leaf sheath. The bud may give rise to a leaf or a tiller.
Fig. 13 - Leaf, node, and bud.
Early tillers arise from the main culm in an alternate pattern. Primary tillers originate from the lowermost nodes and give rise to secondary tillers. Secondary tillers produce tertiary tillers.
Fig. 14 - Primary tillers.
Fig. 15 - Secondary tillers.