Crown gall
(A.S. gealla, gall) A bulbous growth that occurs at the base of certain plants as result of infection, especially by Agrobacterium tumefaciens; a bacterial gene carried by the Ti plasmid is transferred by the bacteria into a higher plant cell, where it causes a tumour-like growth. a.k.a. crown gall tumour. See Agrobacterium; hairy root disease.

Crown
The region at the base of the stem of cereals and forage species from which tillers or branches arise. In woody plants, the root-stem junction. In forestry, the top portions of the tree.

Cryoprotectant
Compound preventing' cell damage d thawing processes. Cryoprotectants are a solubility and low toxicity. Two types of are commonly used: permeating (glycerol and DMSO (q.v))and non-permeating (sugars, dextran, ethylene glycol, polyvinyl pyrolidone and hydroxyethyl starch).

Cryptic
1. Structurally heterozygous individuals not identifiable on the basis of abnormal meiotic-chromosome pairing confifurations (‘cryptic structural hybrids’) 2. A form of polymorphism controlled by recessive gene (‘cryptic polymorphism’) 3. Any mutation which is exposed by a sensitizing mutation and otherwise poorly detected (such mutations probably escape detection because of the plasticity of composition of the. corresponding polypeptide). 4. Phenotypically very similar species (cryptic species) which do not hybridize under normal conditions. 5. Cryptic genetic variation refers to the existence of, for example, alleles conferring high performance for a trait, in a breed that has low performance for that trait.

Culture
A population of plant or animal cells or micro-organisms that i grown under controlled conditions.

Culture alteration
A term used to indicate a persistent change in the properties' of a culture's behaviour (e.g., altered morphology, chromosome constitution, virus susceptibility, nutritional requirements, proliferative capacity, etc.). The term should always be qualified by a precise description of the change which has occurred in the culture.

Culture medium
Any nutrient system for the cultivation of cells of plants, bacteria or other organisms; usually a complex mixture of organic and inorganic nutrients. cf medium.