Talk about glands and canals.

Glands are globular cavities situated in the parenchyma of leaves, stems and fruits (oranges, tangerines, lemons). They are surrounded by cells which excrete the products they elaborate in the glands . When these cavities are not restricted in location, but extend all the length of an organ; they are tube-like spaces, elongated in the longitudinal plane of the organ (leaf, petal, and stem), they are called secretion canals or ducts. In cross section, they appear as circular cavities surrounded by one or two layers of small secretory cells (Example: pine leaves secreting resin).