Of different composition (c.f., heterogeneous = different descent). Pronounce it heterogenous (c.f., heterogeneous). See also: homogeneous, homogenous. Heterosis

The hybrid vigour that is exhibited by the progeny of two inbred (i.e., homozygous) but different parents. This vigour persists for only one generation, and it is the basis of hybrid varieties. Heterozygous

This term refers to a plant whose two parents were genetically different. In plants, the term may refer to a single gene, or to the entire genetic make-up of the individual plant. Heterozygous plants do not 'breed true to type'. See also: homozygous. Hevea brasiliensis

Para rubber. Note that the name comes from the State of Para in Brazil, and that each 'a' is pronounced long, as in 'art'. The name should not be pronounced with each 'a' short, as in 'parachute'.

Para rubber is a deciduous tree native to the Amazon Valley. It was taken to the Far East by the British, and this area became the main producer because it was free of the native pests and diseases. The Brazilian complaint that rubber was stolen from them is not justified in view of their enormous use of Old World crops such as coffee, sugarcane, and soybean. In any event, plantation rubber does not thrive in Brazil, but old plantations, laid out by the Ford Motor Company in the early part of the twentieth century, have resistant survivors and merit screening for vegetative propagation . Hexaploid

A cell or a plant with six sets of chromosomes. Diploid is the normal state in most plants and animals. See also: doubled monoploid, haploid, tetraploid, triploid. Hibiscus cannabis

Kenaf, bimli jute, or Deccan hemp. A jute substitute that probably originated in Africa. Hibiscus esculentis

See: Abelmoschus esculentus. Hippomane manchinella

This is the plant from which arrowhead poisons are extracted in South America. It is of interest in that arrowroot got its name from being a supposed antidote to these poisons.

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