Some Beginnings of Specific Differentiation in Plants

Abstract

Exception is taken to the distorted notion of species gained by those who work with them only in the laboratory. In contrast, a clarified conception of what a species really is may be had by those who will closely observe the organisms in nature. As regards flowering plants, consideration should be given to their plasticity and degree of morphological variation, to their geographic range and to the geologic age of their habitats. Appreciable differences of flowers or fruit are to be regarded as necessary criteria of species in most cases. Examples are given of species superficially almost identical that differ in fruit characters, and of species whose individuals respond tremendously to changes in their environment (amphibious plants). Geographic varieties are species "on the way." Without reproductive differences and with an abundant series of transitions, they have not yet become species. Thoroughly differentiated local species may be successfully sought for in restricted areas which for ages have been ecologically or physiologically unique or which have had long continued geographic isolation.