Bulb, a short, fleshy, and generally conical underground stem, giving off adventitious roots from its under surface, and covered above with leaf-scales. Bulbs are of two classes: squamose, with imbricate scales of small relative width, as in Lilium; and tunicate, with concentrically sheathing scales, as in the onion. Bulbs vary in duration, being either annual, biennial, or perennial, and reproduce themselves, sometimes multiplying rapidly, by the production of "cloves," or axillary buds in the axils of their scales, which become independent. Bulbs are especially characteristic of dry climates, such as Asia Minor and South Africa, and of monocotyledons, especially the Liliaceae and Amaryllidaceae. A swollen aerial branch in epiphytic orchids (q.v.) is termed a pseudo-bulb, but is less closely homologous to a bulb than the aerial bulbil, or undeveloped branch with a few over-lapping leaf-scales, which falls off and reproduces the plant, in the tiger-lily. Enlarged roots, such as those of the turnip, are sometimes erroneously called bulbs by farmers.