Hydrophyte.
(1) Plant whose habitat is water or very wet places, characteristically possessing aerenchyma
(2) Class of Raunkiaer’s Life Forms.

Hydroponics. System of large-scale plant cultivation developed from ‘water-culture’ methods of growing plants in the laboratory, in which their roots dip into a solution of nutrient salts or in which the plants are allowed to root in some relatively inert material, e.g. quartz sand, which is irrigated with the nutrient solution.

Hydrosere. A sere commencing in water or moist sites.

Hymernium. Layer of regularly arranged spore-producing structures found in fruit bodies of many ascomycetes and Basidiomycete fungi.

Hydrotropism.The growth of plant of the perisasc of colonial coelenterates which surrounds and protects the polyp.