The Life Cycle of Plants

Alternation of Generations  -  The fluctuation between the diploid (sporophyte) and haploid (gametophyte) life stages that occurs in plants.

Angiosperm  -  A vascular flowering plant in which seeds are enclosed inside of protective ovaries.

Archegonium  -  The female sex organ of terrestrial plants; where egg cells are produced.

Bryophyte  -  A lower terrestrial plant (often a moss or liverwort) that lacks a vascular system and is dependent on environmental moisture for reproductive and nutritive functions.

Bulb  -  Roughly spherical underground bud containing additional buds that can develop asexually into new plants. A form of vegetative propagation.

Cross-pollination  -  The process, occurring in most angiosperms, by which the male gametes of one plant (carried by pollen grains) fertilize the eggs of another.

Diploid  -  Having two sets of chromosomes, one from each parent.

Double Fertilization  -  The mechanism of angiosperm fertilization that involves the joining of haploid gametes to create a diploid zygote, and the simultaneous joining of a second sperm cell with a fusion nucleus to create a triploid nucleus (which becomes endosperm).

Endosperm  -  A substance, formed from a triploid nucleus in angiosperm reproduction, that nourishes a developing embryo within a seed.

Fragmentation  -  A form of vegetative propagation in which a severed plant part develops into a whole new plant.

Fusion Nucleus  -  The diploid product formed by the joining of the two polar nuclei in the angiosperm ovule.

Gamete  -  A haploid sex cell (either an egg or sperm cell); male and female gametes join during fertilization to create a diploid zygote.

Gametophyte  -  A haploid plant or plant structure that produces haploid gametes through mitosis.

Grafting  -  An artificial form of vegetative propagation in which parts of two young plants are joined together, first by artificial means and then by tissue regeneration.

Gymnosperm  -  A vascular non-flowering plant (commonly known as a conifer) in which seeds are not protected by an ovary.

Haploid  -  Having only one set of chromosomes.

Heterospory  -  The reproductive phenomenon, characteristic of gymnosperms and angiosperms, whereby spores of two distinct sexes are produced; these spores develop into sex-specific gametophytes.

Megaspore  -  Female spore; gives rise to a female gametophyte.

Meiosis  -  Cell division that results in cells with half the chromosomes of the parent cell.

Microspore  -  Male spore; gives rise to a male gametophyte.

Ovary  -  In plants, the protective structure that holds the ovules and surrounds the angiosperm seed; after fertilization, develops into a fruit.

Ovule  -  Structure that contains the female gametophyte and gametes; after fertilization, develops into a seed.

Pistil  -  The female reproductive organ of the flower, composed of a stigma, style, and ovary; sometimes called the carpel.

Polar Nuclei  -  Two nuclei, contained within the same cell, that are created from the mitotic division of the megaspore during angiosperm reproduction; unite in the ovule to form a fusion nucleus, which gives rise to endosperm when fertilized.

Pollen Grain  -  The male gametophyte of gymnosperms and angiosperms.

Pollen Tube  -  The outgrowth of a pollen grain that creates a path through the female sex organ in order to penetrate to the egg cells.

Runner  -  Slender horizontal stem that can give rise, via specialized nodes, to new plants.

Scale Leaf  -  Very small structure on the surface of a tuber that contains a bud from which a new plant can arise.

Scion  -  Twig or bud that is grafted onto a plant with roots (called the stock) and develops into a new shoot system.

Self-pollination  -  The process by which the male gametes of a plant fertilize the eggs of the same plant.

Sporangium  -  The part of a plant where spores are produced.

Spore  -  Haploid cell from which a gametophyte is produced.

Sporophyte  -  A diploid plant or plant structure that produces haploid spores through meiosis.

Stigma  -  The top part of the pistil, where pollen grains are received.

Stock  -  Plant with a root system onto which a twig or bud from another plant (called a scion) is grafted.

Tracheophyte  -  A terrestrial plant with a vascular system.

Triploid  -  Having three sets of chromosomes.

Tuber  -  Fleshy underground storage structure, composed of an enlarged portion of the stem, that has on its surface buds capable of producing new plants.

Vascular System  -  Mechanism of internal water and nutrient transport, characteristic of tracheophytes; made up of the vascular tissues xylem and phloem.

Vascular Tissue  -  A conductive component (either xylem or phloem) of the system that transports food and nutrients throughout the plant body.

Vegetative Propagation  -  A form of asexual reproduction in which plants produce genetically identical offshoots (clones) of themselves, which then develop into independent plants.

Zygote  -  The diploid product of fertilization that develops into an embryo.