The stem and the leaf

The stem grows from the plumule of the seed. It carries nodes (where leaves arise) and internodes (the parts between). On a sugarcane, the rings are the nodes and the pieces between them are internodes. The stem also bears buds at the tip (terminal) and in the angle above each leaf (axillary), and holds up branches, leaves, flowers and fruits. It carries water and minerals up, and food (photosynthates) to other parts.

A leaf grows at a node, with a bud in the angle (axil) above it. Leaves form at the shoot tip in acropetal order: older leaves below, younger ones near the top. A leaf has three parts:

• Leaf base: joins the leaf to the stem. It may carry two small side growths (stipules); in monocots it widens into a sheath around the stem; in some legumes it is swollen, a pulvinus.
• Petiole: the stalk.
• Lamina (leaf blade): with a central midrib, and veins and veinlets branching from it.

The pattern of veins is venation. Veins forming a network is reticulate venation (most dicots, like a mango leaf). Veins running side by side is parallel venation (most monocots, like a banana or grass leaf).

A simple leaf has one blade; any cuts in it do not reach the midrib. A compound leaf is divided into separate leaflets. In a pinnately compound leaf the leaflets sit along a central axis, the rachis (neem). In a palmately compound leaf they spread from the tip of the petiole like fingers (silk cotton). How to tell a leaflet from a leaf: there is a bud in the axil of the whole leaf's petiole, but never in the axil of a leaflet.

Phyllotaxy is the arrangement of leaves on the stem: alternate (one leaf per node: china rose, mustard, sunflower), opposite (a pair at each node, facing each other: Calotropis, guava), or whorled (more than two at a node: Alstonia).