The Ohio Journal of Science

A study of the system of plant relationships inevitably leads to a consideration of the processes through which the system came into existence. Having spent many years in an attempt to learn something of the true phyletic relationships of plants, the writer desires to present, in a series of short papers, some of the remarkable phenomena which have come to light and which apparently have never been published heretofore in any adequate manner. These papers will bear the subtitle, "Studies in Determinate Evolution," so that they can easily be recognized as forming a part of a general presentation. The term, "Determinate Evolution" is used advisedly as expressing the actual condition of things in all evolutionary movements of a fundamental nature. All such primary movements attain a definite limit, sooner or later, beyond which no further movement in the given direction is possible. This broad generalization will be justified when some of the more important evidence has been submitted. All of the more fundamental taxonomic forms, therefore, fall into what will be called orthogenetic series, and these series are the result of progressive and perfective movements, which commonly are profoundly consistent in their development. In general, evolutionary movements are either segregative or progressive. But the segregative mutations are determinative as well as the progressive mutations. Each segregative