lamella (plural, lamellae). Here, a cell structure resembling a plate. Lamellae appear to lay one upon the other, laminarin. A polysaccharide product occurring in the brown algae, late blight. The disease of potatoes and tomatoes caused by the fungus Phytophthora infestans. So-called because it occurs late in the growing season.

lateral conjugation. In algae, a sexual union between neighboring cells of the same filament. Contrast with scalariform conjugation, layering. A method of inducing adventitious root production in a stem while it is still attached to the parent plant. Soil is mounded over the stem.

leaf. An outgrowth from the stem. Involved in photosynthesis. Generally composed of a flattened, green blade attached to the stem by a petiole, leaf trace. Vascular bundle that connects the vascular tissue of the stem with that of the leaf, leaflet. Part of a compound leaf. Distinguished from the leaf by the fact that there is no bud in its axil, legume. A dry fruit that splits along two sutures. The fruit of the bean family, lenticel. A small, lenslike opening in the bark. Said to allow the passage of gases.

leptotene. That stage of the meiotic prophase immediately preceding synapsis and during which the chromosomes appear as fine threads, leucoplast. A colorless plastid.

leucosin. A white substance produced by numbers of yellow-green algae and thought to be a carbohydrate, lichen. A union between a fungus and an alga living together symbiotically.

Grows on rocks and trees, lignin. A constituent of secondary walls, functioning also as an intercellular cement.

linkage. Refers to genes being located on the same chromosome and, thus, passing on their characteristics together, lip cells. In the sporangium of a fern, cells that separate in maturity to allow the escape of spores, lipids. Fats or fatty compounds that are insoluble in water but soluble in certain organic solvents.

lipopolysaccharide. An organic compound made up of lipid and sugar components.

litmus. A compound extracted from several forms of lichens and possessing the quality of being red in acidic solution and blue in alkaline solution, thus used as an indicator, liverwort. A bryophyte. A small, inconspicuous, nonvascular plant. Derives its name from medieval times, when its shape appeared to resemble the lobes of a liver, locule. The cavity of an ovule or anther.

locus. That position on a chromosome associated with a particular genetic trait.

long-day plant. A plant requiring comparatively prolonged periods of light and relatively brief periods of darkness in order to initiate floral primordia.

luciferase. An enzyme that acts upon luciferin to cause the emission of light, luciferin. A pigment that is found in luminescent organisms and furnishes light during oxidation, lumen. A space enclosed by a cell wall. Usually used in reference to dead cells from which protoplast has disappeared, luminescent. Adapted for the production of light, lysis. The disintegration of cells.

lysosome. An organelle bounded by a membrane and containing enzymes capable of breaking down proteins and other molecules.

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