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Glossary: H is for ... hilum hectare habitat.
by Ariadne Unst

Glossary of H...

habitat (n.)
A region or environment where a plant or animal is normally found.

half-life (n.)
Time in which one half of the nuclei in a radioisotope emits its radiation. Half-lives for radioisotopes vary from millionths of a second to billion of years.

haploid (n.)
A cell that contains only one set of chromosomes.

head (n.)
A compact group of flowers in a cluster at the end of a branch; for example a sunflower.

heartwood (n.)
The center of the tree trunk, it is composed of dead xylem cells. (The dead cells are less robust than live cells, so the heartwood sometimes rots, leaving a hollow tree.)

hectare (n.)
An area of 10,000 square meters or 2.47 acres.

hemiparasite (n.)
A parasite like mistletoe; because mistletoe has green leaves, it can photosynthesize; thus it only absorbs nutrients and water from its host.

herbaceous (adj.)
Describing a plant that dies back below the ground each year; fleshy-stemmed; lacks a persistent woody stem.

hilum (n.)
The scar on a seed marking the point of attachment of the ovule.

homology (n.)
a similar character state present in two or more species of organisms, and derived from a single character in their common ancestor. (homologous, adj.)

hot climate (n.)
Mean annual temperature over 21ºC. Usually:
Rain forest in equatorial and tropical marine climates.
Savanna in continental regions.
Also see climate.

humus (n.)
Dark partly soluble organic substance formed by the decomposition of organic soil matter.

hybrid (n.)
Plant (or animal) produced by interbreeding two species. "natural hybridizing between species of pitcher plants tends to increase when the plants are under environmental pressure ... Hybridizing occurs frequently between species in the same genus, but because most fail to reproduce tru to type they eventually disappear ... hybridizing is an important means by which plants evolve new species that are able to compete outside their original habitat, thus enlarging the range of the genus" [ Jane Scott].

hypocotyl (n.)
The part of the central axis portion of a plant seedling that is below the cotyledons.

hypogynous (adj.)
Growing on the under surface, like a fungus beneath a leaf.
Also having stamens, petals, and sepals attached below the ovary.
Compare with epigynous.

hypogeous (adj.)
Growing or developing below the soil surface.