The pseudobulb is a storage organ found in many epiphytic and terrestrial sympodial orchids. It is derived from a thickening of the part of a stem between leaf nodes and may be composed of just one internode or several, termed heteroblastic and homoblastic respectively. All leaves and inflorescences usually arise from this structure. Pseudobulbs formed from a single internode produce the leaves and inflorescence from the top, while those that are formed from several internodes can possess leaves along its length. The modified sheath leaves that appear at the base of a pseudobulb and often enfold all or part of it are usually dry and papery, though in some orchids the sheaths bear leaf blades and the leaves at the pseudobulb's apex are reduced to scales.