=724. The bulb.=—The bulb is in the form of a bud, but the scale leaves are large, thick, and fleshy, and contain stored in them food products manufactured in the green aerial leaves and transported to the underground bases of the leaves. Or when the bulb is aerial in its formation, it is developed as a short branch of the aerial stem from which the reserve food material is transported. Examples are found in many lilies, as Easter lily, Chinese lilies, onion, tulip, etc. The thick scale leaves are closely overlapped and surround the short stem within (also called a _tunicated_ stem). In many lilies there is a sufficient amount of food to supply the aerial stem for the development of flower and seed. There are roots, however, from the bulb and these acquire water for the aerial shoot, and when planted in soil additional food is obtained by them. [Illustration: Fig. 425. Bulb of hyacinth.] [Illustration: Fig. 426. Corm of Jack-in-the-pulpit.] =725. Corm.=—A corm is a thick, short, fleshy, underground stem. A good example is found in the jack-in-the-pulpit (Arisæma). =726. Tubers.=—These are thickened portions of the subterranean stems. The most generally known example is the potato tuber (“Irish” potato, not the sweet potato, which is a root). The “eyes” of the potato are buds on the stem from which the aerial shoots arise when the potato sprouts. The potato tuber is largely composed of starch which is used for food by the young sprouts. =726=_a_. =Phylloclades.=—These are trees, shrubs, or herbs in which the leaves are reduced to mere bracts and stems, are not only green and function as leaves, but some or all of the branches are flattened and resemble leaves in form as in Phyllanthus, Ruscus, Semele, Asparagus, etc. The flowers are borne directly on these flattened axes. The prickly-pear cactus (Opuntia) is also a phylloclade. Examples of phylloclades are often to be found in greenhouses. =727. Undifferentiated stems= are found in such plants as the duckweed, or duckmeat (Lemna, Wolffia, etc. See Chapter III). IV. Annual Growth and Winter Protection of Shoots and Buds.[41]