In ____ the leaf base expands into a sheath covering the stem partially or wholly.

Step-by-step solution

Leaf base is the lowest part of the leaf found near the petiole. It has uses in classification and identification of the plant as it greatly varies from plant to plant. In many plants, like monocotyledons, it gets modified by expanding itself into a sheath which partially or wholly covers the stem. This covering is found to be at some distance above the node and is usually found in plants like Zea mays , sugarcane, wheat etc. When the leaf base is swollen in some leguminous plants it is known as the pulvinus.