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Glossary
nastic movement a movement of a plant part (such as a leaf) not caused by an external stimulus natural selection the action of the environment on organisms such that those individuals better able to survive environmental stress are more likely to reproduce and perpetuate their species necrosis the death of a plant tissue nectar a sugary fluid secreted in some flowers nectar guide a contrasting color pattern in a flower that guides a pollinator to the nectar nectary a gland secreting nectar nitrogen cycle the circulation of nitrogen between the environment and living organisms nitrogen-fixation the conversion of atmospheric nitrogen gas into organic nitrogen compounds by a limited number of microorganisms node the segment of a stem to which leaves and axillary buds are attached N-P-K ratio the relative proportions of nitrogen, phosphorus, and potassium in a fertilizer nucleus the body within a cell controlling its activities, including inheritance organ a part of a plant, composed of different tissues, that acts as a functional unit organelle a cell structure performing a specific function organic referring to substances containing both carbon and hydrogen organism a living plant or animal osmosis the diffusion of water across permeable cell membranes that select for or against specific substances ovary the basal portion of a pistil that becomes a fruit ovule an immature seed palisade cell a photosynthetic cell directly beneath the upper leaf epidermis palmate venation a vein pattern in which the major veins radiate from one point
palmately compound leaf a leaf in which the leaflets radiate from one point panicle a highly branched inflorescence parallel venation a vein pattern in which the veins are arranged parallel to each other parasite a plant or animal obtaining food from another living organism, frequently to the latter’s detriment parenchyma a thin-walled, undifferentiated cell parthenocarpy development of a fruit without pollination, fertilization, or seed development pectin a substance in cell walls binding cells together pedicel the stalk of an individual flower in an inflorescence perennial a plant living through several growing seasons perianth all the sepals and petals in a flower pericarp the fruit wall; derived from the ovary wall pericycle a root tissue giving rise to branch roots petal an often flattened, conspicuously colored flower part petiolate leaf a leaf in which the blade is attached to the stem by a petiole petiole a leaf stalk pH a measure of relative acidity or alkalinity phenotype the physical appearance of an organism phloem the food-conducting tissue of plants photoinduce to initiate a physiological process as a result of being subjected to a particular photoperiod photoperiodism the initiation of flowering in response to relative lengths of day and night photosynthesis the process in which light energy is used to form foods from carbon dioxide and water phototropism curvature of a plant organ in response to light phytoalexin a chemical produced by a plant to inhibit the growth of pathogens
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