This nomenclature uses the numbers of the binomial expansion (i.e., 20, 21, 22, 23, etc., with arithmetic values of 1, 2, 4, 8, etc.). Each binomial number has an arithmetic value that is double that of its predecessor. The sum of any combination of binomial numbers is unique. For example, the sum 21 can be obtained only by adding 16 + 4 + 1, and no other combination of binomial numbers can add up to this sum. The nomenclature can be applied to matching pairs of vertical genes. Each pair of matching genes is then labelled with the binomial numbers 1, 2, 4, 8, etc., in order of discovery. The name of each pair of genes is the primary Habgood name, and it is a single binomial number. Any combination of genes is named with the sum of their binomial numbers, and this is a secondary Habgood name. It will be seen that any combination of genes, in either the host or the parasite, is named with a single number, and that exactly matching vertical resistances and vertical parasitic abilities have the same name. The composition of a secondary Habgood name is easily determined. Suppose the secondary name was 29. The largest possible binomial number is subtracted from it. In this case, this would be binomial 16. This means that gene 16 is present. The remainder is 13, from which 8 can be subtracted, indicating that gene 8 is present. The remainder is now 5, showing that genes 4 and 1 are also present. These gene names 16 + 8 + 4 + 1 add up to 29, and no other combination of binomial numbers can add up to this sum. Habitat
The natural home of an organism, usually with living conditions that are closely similar to those of its original environment. Hand-pollination
The artificial pollination of a flower, usually involving cross-pollination in order to obtain a sexual recombination of two chosen parents. See also: Emasculation. Haploid
A cell or plant that has only one set of chromosomes. A sex cell (i.e., pollen and ovules in plants, sperm and ova in animals) is normally haploid, and the fusion of two sex cells produces a normal diploid with two sets of chromosomes. Haploid plants can be produced artificially, and their single set of chromosomes can be doubled to produce a doubled monoploid. The terms haploid and monoploid are synonymous. See also: tetraploid, triploid. Hardy-Weinberg law
The law that states that gene frequencies will remain constant from generation to generation, provided that no other factors, such as selection or mutation, are operating. Hardwoods
Timber trees that are Dicotyledons . The timber of these trees is suitable for fine furniture and cabinet making. See also: Softwoods. Haricot bean
See: Phaseolus vulgaris. Harvesting
The process of gathering in a crop. Commercial harvesting of grain crops is usually undertaken with a combine harvester. Many horticultural crops, and all subsistence crops are harvested by hand. The harvesting of a plant breeder's screening population usually involves carefully selected individual plants. Hashish
See: Cannabis sativa. Hay
Pasture grasses and/or pasture legumes that have been cut and dried in the field for use as animal feed. "Making hay while the sun shines" is a traditional method of providing winter-feed for farm livestock. Hazel nut
See: Corylus avellana. Head to row selection See: Family selection. Hectare
A measure of land area. One hectare is 10,000 square metres, or 2.471 acres. Helianthus annuus
The sunflower, which is now a valuable oil crop. The Church in Russia forbade the use of a long list of cooking oils on many fast days each year. Being an unknown New World plant, sunflower was not on that list of proscriptions. It consequently became very popular in Russia where the first cultivars were developed. Dwarf varieties are now grown for combine harvesting in many countries. The species is open-pollinated and amenable to selection for horizontal resistance by amateur breeders Sunflowers, and the closely related Jerusalem artichoke, are the only crop species of any significance to originate in North America. Helianthus tuberosus
The Jerusalem artichoke. A close relative of the sunflower, it is open-pollinated and amenable to recurrent mass selection for horizontal resistance by amateur breeders who might have a special interest in this rather unimportant crop. Heliotropic
(= phototropic) A directional growth or movement towards light.
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