Anatomy Of Flowering Plants

In winter, when the cambium is less active and forms fewer xylary elements that have narrow vessels then this wood is called autumn wood or late wood. While, in spring season, cambium is very active and produces a large number of xylary elements having vessels with wider cavities, this wood is called spring wood or early wood.

Medullary ray is any of the vertical plates of parenchyma cells running radially through the cylinder of vascular tissue in the stems and roots of plants. Each may be one to many cells in width. Primary medullary rays occur in young plants and in those not showing secondary thickening; they pass from the cortex through to the pith. Secondary medullary rays are produced by the vascular cambium and terminate in xylem and phloem tissues. Medullary rays store and transport food materials.

In monocot leaves, both the surfaces contain stomata. The leaf is therefore amphistomatic.
Each stoma is lined by a pair of dumb bell-shaped guard ceils.