| calcium carbonate (CaCO3) | A compound found in limestone, ashes, bones, and shells, the primary component of lime. |
| callus | Tissue that develops when cambium or other meristematic tissue is wounded. |
| calorie | Amount of heat required to raise the temperature of 1 cubic centimeter of water 1°C. |
| calyx | The collective term for the sepals (the cup, usually green, between a flower and its stem). |
| cambium | The living, growing layer of cells between the xylem and phloem. In woody plants, it is located just beneath the bark. |
| candelabrum | A strong, dominant rose cane with accelerated growth that originates from a bud union and explodes with many blooms. |
| candle | On a pine tree, new terminal growth from which needles emerge. |
| cane | The externally woody, internally pithy stem of a bramble or vine. |
| canker | A localized lesion on a limb or trunk, usually due to disease or injury. Part of the bark or wood appears to be eaten away or is sunken. |
| canopy | (1) The top branches and foliage of a plant. (2) The shape-producing structure of a tree or shrub. |
| capillary force | The action by which water molecules bind to the surfaces of soil particles and to each other, thus holding water in fine pores against the force of gravity. |
| capillary water | Water held in the tiny spaces between soil particles or between plant cells. |
| capitulum | (1) A dense, short, compact cluster of sessile flowers (stalkless and attached directly at the base), as in composite plants or clover. (2) A very dense grouping of flower buds, as in broccoli. |
| carotene | A orange-yellow pigment located in the chloroplasts. |
| caterpillar | See larva. |
| catfacing | Disfigurement or malformation of a fruit. Fruits typically affected include tomatoes and strawberries. Although not fully understood, catfacing is thought to be caused by insects or adverse weather during fruit development. |
| cation | A positively charged ion. Plant nutrient examples include calcium (Ca++) and potassium (K+). See anion. |
| cation exchange capacity (CEC) | A soil’s capacity to hold cations as a storehouse of reserve nutrients. |
| cell | The smallest structure in a plant. |
| central leader | (1) A trunk or stem extending up through the axis of a tree or shrub and clearly emerging at the top. (2) A system of pruning that uses the central leader as a basic component. |
| cell wall | The outer covering of a plant cell. |
| cellular respiration | The chemical breakdown of food substances, resulting in the release of energy. |
| cellulose | A plant substance forming part of the cell wall. |
| cercus | A thread-like or sometimes forceps-like tail near the tip of an insect’s abdomen (usually a pair). Plural: cerci. |
| chelate | A complex organic substance that holds micronutrients, usually iron, in a form available for absorption by plants. |
| chlorophyll | The green pigment in plants. Responsible for trapping light energy for photosynthesis. |
| chloroplast | A specialized component of certain cells. Contains chlorophyll and is responsible for photosynthesis. |
| chlorosis | An abnormal yellowing of a leaf. |
| chromosome | A threadlike structure within each living cell which contains the cell’s genetic material. |
| cladode | A flattened stem performing the function of a leaf, as in a cactus pad. |
| clay | The smallest type of soil particle (less than 0.002 mm in diameter). |
| climber | A plant that climbs on its own by twining or using gripping pads, tendrils, or some other method to attach itself to a structure or another plant. Plants that must be trained to a support are properly called trailing plants, not climbers. |
| cloche | A plastic, glass, or Plexiglas plant cover used to warm the growing environment or protect plants from frost. |
| clone | A plant group whose members have all been derived from a single individual through constant propagation by vegetative (asexual) means, e.g. by buds, bulbs, grafts, cuttings, or laboratory tissue culture. |
| C:N ratio | The ratio of carbon (C) to nitrogen (N) in organic materials. Materials with a high C:N ratio (high in carbon) are good bulking agents in compost piles, while those with a low C:N ratio (high in nitrogen) are good energy sources. |
| cold composting | A slow composting process that involves simply building a pile and leaving it until it decomposes. This process may take several months or longer. Cold composting does not kill weed seeds or pathogens. |
| cold frame | A plastic-, glass-, or Plexiglas-covered frame that relies on sunlight as a source of heat to warm the growing environment for tender plants. |
| cold hardening | The process where plants prepare for low temperatures. |
| cole crops | A group of vegetables belonging to the cabbage family; plants of the genus Brassica, including cauliflower, broccoli, cabbage, turnips, and brussels sprouts. |
| coleoptera | An insect family made up of species having horny front wings that fit over their hindwings. Includes beetles and weevils. |
| collar | A swollen area at the base of a branch where it connects to a trunk. Contains special tissue that prevents decay from moving downward from the branch into the trunk. See shoulder ring. |
| compaction | Pressure that squeezes soil into layers that resist root penetration and water movement. Often the result of foot or machine traffic. |
| companion planting | The practice of growing two or more plants together in the hope that the combination will discourage disease and insect pests. |
| compatible | Different varieties or species that set fruit when cross-pollinated or make a successful graft union when integrated. See pollinizer. |
| complete flower | A flower having all of the normal flower parts. |
| complete metamorphosis | A type of insect development in which the insect passes through the stages of egg, larva, pupa, and adult. The larva usually is different in form from the adult. See simple metamorphosis. |
| composite head | An inflorescence composed of many tightly packed, small, ray and disc flowers. |
| compost | The product created by the breakdown of organic waste under conditions manipulated by humans. Used to improve both the texture and fertility of garden soil. See humus. |
| compound bud | More than one bud on the same side of a node. Usually, unless growth is extremely vigorous, only one of the buds develops, and its branch may have a very sharp angle of attachment. If it is removed, a wider angled shoot usually is formed from the secondary (accessory) bud. Ashes and walnuts are examples of plants that typically have compound buds. |
| compound leaf | A leaf in which the blade is divided into separate leaflets. |
| conifer | A cone-bearing tree or shrub, usually evergreen. Pine, spruce, fir, cedar, yew, and juniper are examples. |
| conk | A fungal fruiting structure (e.g., shelf or bracket fungi) formed on rotting woody plants. |
| contact pesticide | A pesticide that kills on contact. |
| cordon | (1) A method of espaliering fruit trees, vines, etc. to horizontal, vertical, or angles wire or wooden supports so maximum surface is exposed to the sun, resulting in maximum fruit production. (2) A branch attached to such a support. |
| cork | The protective outer tissue of bark. |
| cork cambium | A layer of cells in the cambium that gives rise to cork. |
| corm | An underground storage organ consisting of the swollen base of a stem with roots attached to the underside. Crocus and gladiolus are examples of plants that form corms. See bulb, tuber, rhizome. |
| cormel | A small, underdeveloped corm, usually attached to a larger corm. See bulbil and bulblet. |
| cornicle | A short, blunt horn or tube (sometimes button-like) on the top and near the end of an aphid’s abdomen. Emits a waxy liquid that helps protect against enemies. |
| corolla | Collectively, all of a flower’s petals. |
| cortex | Cells that make up the primary tissue of roots or stems. |
| corymb | A usually flat-topped flower cluster in which the individual flower stalks grow upward from various points on the main stem to approximately the same level. |
| cotyledon | A seed leaf; the first leaf from a sprouting seed. Monocots have one cotyledon; dicots have two. |
| cover crop | A crop dug into the soil to return valuable organic matter and nitrogen to the soil. Legumes such as clover, cowpeas, and vetch are common cover crops. Also called green manure. |
| cross-pollination | The fertilization of an ovary on one plant with pollen from another plant, producing an offspring with a genetic makeup distinct from that of either parent. See pollenizer. |
| crotch angle | The angle formed between a trunk and a main scaffold limb. The strongest angle is 45° to 60°. |
| crown | (1) Collectively, the branches and foliage of a tree or shrub. (2) The thickened base of a plant’s stem or trunk to which the roots are attached. |
| cultivar | A specially cultivated variety of a plant that most often is reproduced vegetatively. For example, ‘Transparent’ is a cultivar of apple. See variety. |
| cuticle | (1) A relatively impermeable surface layer on the epidermis of leaves and fruits. (2) The outer layer of an insect’s body. |
| cutin | (1) A waxy substance on plant surfaces that tends to make the surface waterproof and can protect leaves from dehydration and disease. (2) A waxy substance on an insect’s cuticle that protects the insect from dehydration. |
| cutting | A piece of leaf, stem, or root removed from a plant and prompted to develop into a new plant that is genetically identical to the parent plant. |
| cyme | A flower stalk on which the florets start blooming from the top of the stem and progress toward the bottom. |
| cyst | The swollen, egg-containing female body of certain nematodes. Can be seen on the outside of infected roots. |
| cytokinin | A plant hormone primarily stimulating cell division. |
| cytoplasm | The living protoplasm of a cell, excluding the nucleus. |
| cytoplasmic membrane | The membrane enclosing the cytoplasm. |
