Back to Glossary A - Z

Calyx A term referring to the sepals collectively, It is the first of the series of floral parts and is usually green and leaflike but may be colored like the petals. (Nelson, 2003) Diagram of calyx.

Cambium A zone or cylinder of meristematic (dividing) cells located between xylem and phloem tissues in plants. The cambium cells divide to form new xylem and phloem cells. (Nelson, 2003) See diagram of cambium.

Cation Exchange Capacity (CEC) A measure of the ability of an absorbing material such as a root medium to hold exchangeable cations-for example, various fertilizer, nutrients, including ammonium nitrogen, potassium, calcium, magnesium, iron, manganese, zinc, and copper. CEC is generally measured in milliquivalents per 100 cubic centimeters (me/100 cc) of dry absorbing material, and a value of 6-15 me/100 cc is considered ample for greenhouse root media. A root medium with low CEC does not retain nutrients well and consequently must be fertilized often. (Nelson, 2003)

Central heat system A heating system in which the heat used for heating one or several greenhouses is generated in a single location in one or more boilers. (Nelson, 2003) Excellent on-line review of heating systems.

Chelate A chemical complex that will hold or bind a metal. Metals that are commonly chelated for agricultural use are less subject to tie-up in adverse root-media environments. These metals include iron, manganese, zinc, and copper. (Nelson, 2003). Field example of helpfulness of applying chelated metals.

Chloropicrin Tear gas. A chemical used for pasteurizing greenhouse root media. It is not as popular as methyl bromide but can be used in carnation root media. (Nelson, 2003) Pesticide Factsheet for chloropicrin.

Chloroplast A specialized body (organelle) in the cytoplasm of some plant cells that contains chlorophyll. (Nelson, 2003) Review of chloroplast basics.

Chlorosis The state in which normally green plant tissue is lighter green and possible yellow due to the loss of chlorophyll or the failure of chlorophyll to form. (Nelson, 2003) Some nutrient deficiencies can cause chlorosis.

Chord A support member of the greenhouse frame that is under tension. (Nelson, 2003)

Clay A mineral component of soils consisting of particles less than 0.002 mm in diameter. (Nelson, 2003)

Closed cultural system Any method for growing plants in which the nutrient solution is recirculated. Nutrients are not allowed to leach from the pot or bench to the ground. (Nelson, 2003)

Conduction heat loss Heat loss by transmission through a barrier such as the covering of a greenhouse. (Nelson, 2003)

Conidiophore A specialized hypha on which one or more conidia are produced. (Nelson, 2003)

Conidium (plural, conidia) An asexual fungus spore formed from the end of a conidiophore. (Nelson, 2003)

Container capacity The maximum amount of water a root medium can hold against the force of gravity when this root medium is in a container that has open drainage holes in its base. (Nelson, 2003)

Convection heat loss Loss of heat from the greenhouse as it moves in air convection currents to the greenhouse covering, then through the covering by conduction, and finally away from the outside of the covering. (Nelson, 2003)

Convection heater A heater that does not contain a heat exchanger. Heat leaves the heater in the smoke. The smoke is carried the length on the greenhouse in a pipe that serves as an exchanger as heat passes through its walls to the greenhouse air. (Nelson, 2003)

Corporation A legal entity, separate and distinct from the persons (stockholders or shareholders) who own it. The corporation has all the rights and responsibilities of a person and may buy, own, and sell property; sue and be sued; and enter into contracts with both outsiders and its own shareholders. The most important advantage of the corporate form is its responsibility for its own acts and debts and the freedom of its owners from liability for either. (Nelson, 2003)

Cost accounting The use of the cost data of producing a given product for the purpose of assessing and controlling those cost. Since a knowledge of costs and controlling costs is vital to good management, a large greenhouse firm often engages the services of a cost accountant. (Nelson, 2003)

Critical night length The length of darkness less tan which a short-night plant or more than which a long-night plant will undergo a photoperiodic response. The critical night length varies with plant species an even sometimes with cultivars within a species. (Nelson, 2003) Learn more about photoperiod control in greenhouses.

Cross-fluted cellulose pad An evaporative cooling pad composed of laminated sheets of fluted (corrugated) cellulose impregnated with insoluble antirot salts, rigidifying saturants, an wetting agents. Pores are oriented diagonally through the pad in two directions, crossing each other. (Nelson, 2003) Here is an example of a cross-fluted cellulose cooling pad located in a research greenhouse at the University of Vermont. As you might imaging these wet pads in warm summer temperatures can ideal environments for algae and other microbes some of which can impact human health. Often biocide treatment is required.

Crown bud A flower bud whose development has ceased. It sometimes develops the appearance of a crown. Generally, this cessation of development breaks apical dominance, resulting in the development off side shoots. Crown buds may be caused by excessively low or high temperatures or in long-night plants by a series of short nights while the flower bud is developing. (Nelson, 2003)

Cultivar A cultivated variety. A cultivar usually has less variation within it than does a botanical variety. (Nelson, 2003) Learn more about the cultivar concept and the language of horticulture.

Curtain wall The nontransparent lower portion of the side walls of a greenhouse. (Nelson, 2003)

Cut Flowers Sometimes referred to as fresh flowers. Flowers collected and sold with the roots (and somtimes a portion of the stem) removed. Almost always requires access to refrigerated transport.

Cuticle A nonliving waxy layer covering all plant cells that are in contact with air. Although this layer protects plant cells from drying, water and nutrients can slowly penetrate. (Nelson, 2003)

Cuttings The portion of a plant removed for the purpose of asexual propagation. It may be part of a stem, a leaf, or part of a root, depending on the species of plant to be propagated by removing terminal stem pieces and placing the lower inch of them in a rooting medium in a moist environment to induce new root formation. (Nelson, 2003)

Cyclic lighting An alternative method of applying light during the night to achieve the photoperiodic effect of long days. The customary lighting period is divided into a number of subperiods, each comprised of a duration of light followed by darkness. The total duration of light can be reduced by as much as 80 percent. Where three hours of light are customarily applied, six consecutive cycles of 5 minutes of light and 25 minutes of darkness can be substituted, thereby reducing electrical consumption greatly. (Nelson, 2003)