 Mendelian genetics provides laws that govern the passing on of discrete traits from one generation to the next. For example, Mendel experimentally demonstrated particular patterns of inheritance for smooth and wrinkled peas in a population of pea plants. Discrete or discontinuous traits contrast with continuous or quantitative traits. Height in humans and leaf number in trees are continuous traits. Continuous traits vary on a continuum that can be represented as a normal distribution, graphed as a bell curve. Most philosophical discussion about heredity and heritability arises from the study of continuous traits.