Acid- Refers to a material (soil, potting mixture, water, etc.) with a pH level below 7.0. Acidity is an indication of the absence of lime or other alkaline material. See also neutral and pH.

Active growth period- The period within each 12-month season (not necessarily a calendar year) when a plant continues to put out new leaves, increases in size, and, generally, produces flowers. Compare dormancy and rest period

Aerial roots- Roots that arise in the air, from stems not necessarily in contact with a surface. Aerial roots are often capable of clinging to trees and other supports, and they can usually absorb moisture from the air.

Alkaline- Refers to a material (soil, potting mixture, water, etc.) which has a pH level above 7.0. Alkalinity can be an indication of the presence of lime. The opposite of acid. See also neutral and pH.

Alternate- Refers to the placement of leaves on a stem. Alternate leaves are borne singly at different heights, more or less alternating from one side of the stem to the other. Compare opposite.

Annual- A plant that grows from seed to flower and seed production and then dies within a single growing season. Compare biennial and perennial.

Anther- The part of the flower that produces pollen (the male sex cells). Anthers are often carried on a long filament, and the combined organ is known as a stamen.

Areole- An organ unique to the cactus family. A modified sideshoot, the areole is usually cushionlike and carries hairs and/or spines. From the areoles arise flowers and offsets; each areole flowers only once.

Axil- The angle between the leaf or leaf stalk and the stem that carries it. Any new growth or flower bud that arises from an axil is called axillary.

Biennial- A plant that grows from seed to flower and seed production and then dies during two growing seasons. Coinpare annual and perennial.

Bigeneric- Refers to a hybrid plant derived from the crossing of parents from two distinct genera. See also intergeneric.

Bipinnate- Refers to leaves that are doubly pinnate-that is, divided into segments that themselves have segments. See also pinnate.

Bloom- (1) An easily smudged powdery or waxy coating, generally whitish or bluish, found on certain leaves and fruits. (2) A synonym for flower.

Bract- A modified leaf often part of a flower, which may be either leaflike or petallike and is sometimes highly colored and long-lasting.

Bud- A condensed shoot, often protected by overlapping scales. A growth bud contains embryo leaves. A flower bud contains embryo flowers or flower clusters.

Bulb- A storage organ that usually grows underground and resembles a bud in that it contains the embryo leaves and sometimes flowers of the plant. Bulbs, which enable many plants to endure prolonged periods of total inactivity (dor- mancy), often have a protective skinlike covering (the tunic).

Bulbil- An immature, miniature bulb formed by certain bulbous plants either at the base of mature bulbs or on the stems. The word is sometimes applied loosely to miniature tubers, as in some begonias, or to leafy plantlets with smaller bases, as in certain ferns.

Calyx- The outermost part of a flower, which can consist of separate sepals or be fused into a singer organ. The calyx is normally tough and green and protects the corolla within. In some plants, however, it is brightly colored and resembles the corolla.

Channeled- Hollowed like a gutter. Usually used in reference to long, narrow leaves with upturned edges, but the word is also used to describe stems that are hollowed on one side to form a channellike depression.

Chlorosis- A condition in which leaves become unnaturally pallid, whitish, or yellow. The disease is usually due to lack of essential minerals.

Column- An organ in which male and female parts of the flower are fused together. The column is a major identifying characteristic of orchids.

Compound- Refers mainly to leaves that are divided into two or more segments, but can also refer to flowers or fruits composed of several similar parts. The opposite of simple.

Corm- A solid underground storage organ formed from the thickened base of the stem, usually with a protective covering of papery scales (the tunic).

Corolla- The part of the flower that is usually its major decorative feature. It may consist of separate petals or be more or less fused into a single unit. The corolla tends to be colorful, in contrast to the normally plain green calyx.

Cotyledon- The first leaf or leaves to be carried by a seedling after germination. Cotyledons are often different in appearance from subsequent and adult leaves.

Cristate- Crested, or cockscomb shaped. Refers to abnormal-looking cockscomblike growth in one area of leaves, stems, or flowers. Varieties of house plants with cristate-leaved forms exist among the ferns, and cristate stemmed forms are found among cacti and a few succulents.

Crown- The area at the base or center of a herbaceous perennial from which top growth and roots emerge. The crown is the part of the plant where shoots and roots meet.

Cultivar- Usually a variety that has originated in cultivation rather than in the wild. Cultivar plant names are generally in a modern language, not Latin, and are correctly enclosed within single quotation marks. See also variety.

Cutting- A portion of stem, leaf or root, or sometimes an entire leaf removed from a plant and treated in such away that it produces roots and eventually grows into a new plant.