Incubation Period - The time between the inoculation with a pathogen, and the development of symptoms.

Incubous - Used for describing the leaf of a liverwort, when its upper border, (i.e., the border towards the apex of the 'stem') is overlapping the lower border of the next leaf above it, and on the same side of the stem.

Incumbent - (1) Lying on. (2) Said of a radical which is bent back to lie on one of the cotyledons.

Indefinite Growth - Means the ability of certain plants or plant organs to grow without limit continuously for indefinite period, e.g., trees and leaves of monecotyledons.

Indefinite Inflorescence - See racemose inflorescence.

Indehiscent - Said of a fruit or fruiting body that does not open to desperse its contents. Such bodies are probably believed to have developed from suppression of naturally occurring opening mechanisms which are found in dehiscent structure.

Independent Assortment - Used for the separation of alleles of a pair during meiosis independently of the separation of alleles of another pair in the organism. Hence, in a heterozygote, for two characters AbBb, four types of gamets get formed after meoisis having equal frequencies AB,Ab,aB,ab). The law of independent assortment was given by Mendel (second law of Mendel) but it holds true only when two genes are not linked.

Indicator Plant - A plant growing under special conditions of climate, or in a particular soil, or in a particular community, and thus, by its presence, indicates the general nature of the habitat.

Indifferent Species - A species occurring in two or more distinct communities.

Indigenous - Native to an area which is not introduced.

Induced Enzyme - (adaptive enzyme). An enzyme which gets synthesized in response to high concentration of its substrate (See induction). In absence of substrate, genes governing enzyme synthesis get repressed.

Induction - A substance promoting the activity of a gene or a group of genes.

Induction - A process in which denovo synthesis of an enzyme or group of enzymes gets stimulated by the presence of substrate in the cell e.g., there occurs an increase ingalactossidease synthesis in cells of E. coli when cells have been supplied with lactose as the sole carbon source.

Indumentum - Said of the dense or sparse convering usually of hairs.

Indusium - Said of flap like covering of tissue which partially or completely covers the sporangia in a sours in certain ferns. It may be outgrowth of placenta (true indusium)or formed by curving of laminar margin (False indusium).

Inferior Ovary - Used for describing condition of ovary in angiospermic flower in which sepals, petals and stamens get inserted above the level of ovary.

Inflorescence - Said of the system which consists of more than one flower in many angiosperms in which flowers are borne on a special inflor science axis, separated from vegetative parts by an extended internode.

Infraspecific Variation - Used for describing the difference in appearance exhibited by individual members of the same species or breeding population due to either environmental influences such as nutrition competition, seasonal effects etc., or due to genetic factors such as the genetic recombination and mutation.

Infructescence - Used for describing the inflorescence after the flowers have fallen, and the fruits get formed.

Infundiluliform - Tubular below, gradually opening upwards, i.e., funnel-shaped.

Inhibitor - A substance limiting or destroying the catalytic activity of an enzyme.

Initial (initiating cell, meristematic cell). Used for describing any actively dividing cell in a meristem. After each division in initial, one daughter cell retains meristematic activity to form new initial while other daughter cell differentiates to form a cell in the plant body. The initials are usually having a dense cytoplasm.

Initial Cell - A cell which remains meristematic, divides repeatedly, and, gives rise to many daughter-cells, from which, after further division, the permanent tissues of the plan t get differentiated.

Innovation. (1) An accessory branch which is produced in some mosses, after the sporangium get developed.
(2) A newly formed shoot which is formed during one season.
Inoculation - (1) The conveyance of an infection to a host plant by any means of transmission.
(2) The entry of the germ tube of a parasitic fungus into a host.
(3) The placing of spores, or piece of mycelium of growing fungi, or bacteria, into a culture medium.

Inoculum Potential - The energy of growth of a fungus, or other microorganism which is available for the colonization of a substrate.

Insecticide - Any chemical killing insects. The term is usually applied to chemicals that kill mites, nematodes and other invertebrate pests.

Insectivorous Plant (carnivorous plant). A plant adapted to derive food by trapping, killing and digesting small animals in addition to normal photosynthesis. Such plants generally occur in areas of nitrate deficiency particularly. Examples are Drosera, Nephenthes etc.

Integument - Said of protective structure that develops from the base of an ovule and encloses it almost completely except at an opening at the tip of nucleus (at micropyle).

Integument - (1) The membrane(s), enclosing the nucellus, finally forming the test
. (2) The membrane enclosing the female gameteophyte in the Lepidocarpales.

Interaction of Genes - Used for describing the process by which one gene-difference affects the expression of another genedifference.

Interbreeding - Experimental hybridization involving different species or varieties.

Intercalary - (1) Describing a meristem occurring between non divid in tissue.
(2) Lying between other bodies of a row, or placed somewhere along the length of a stem, filament, or hypha.