Figure 3. Diagrammatic presentation of the morphs of several taxa within the genus Desmodesmus, organisms formerly called Scenedesmus (see text). The layered cake would represent some, or all if one wished, of the members within the genus. For comparative purposes similar morphologies, such as quadricaudates, are positioned in one layer, with a gradation of layers from more spiny cells (top) to spineless (bottom). A slice of the cake would represent a plastic species, one growing in a fluctuating environment. That slice, whether a, b or c, has a number of morphologically different forms, each produced in response to a specific environmental signal. Arrow, in potential slice a, indicates production of an additional multispined, colonial morph when the signal was a spring low temperature.