The Telome Theory

Abstract

Morphologists have long been concerned with the fundamental nature of the vascular plant body-with the relationships between root, stem and leaf, and with the origin of reproductive structures. Attempts at analysis on the basis of either formal or phyletic morphology have given rise to a number of theories dealing with the organization of the plant body. Those related to the flowering plants are summarized by Arber (1930) and need not concern us here, since they are of historical interest only. A theory which encompasses a consideration of all vascular plants, and which is based primarily upon studies of the lower Tracheophyta, recent and fossil, has had greater vitality-so much so, indeed, that it has permeated the thinking of many morphologists and paleobotanists to a degree not realized by those who have not followed the literature in these fields. This is the telome theory, perhaps better termed the " telome concept". Among other aspects the telome concept has assisted in a clarification of our ideas on the relationships between root, stem and leaf, and emphasizes that the plant body is an axis, with a descending portion, the root, and an aerial portion, the shoot, whose appendages are merely modified parts of the stem. Before considering the telome theory itself, it is desirable to point out that, like many another concept, it did not arise de novo, but was foreshadowed by the work of earlier investigators. Reference will repeatedly be made to a fundamental principle advocated by all of these workers which is an essential part of the telome theory itself. This is the principle of overtopping, shown diagrammatically in its simplest form in Fig. 1. This principle involves the belief that the oldest method of branching was dichotomous (a dichopodium). If, at each fork, one of the two branches becomes stronger than the other, a sympodium will result, with an apparent main axis composed of one of the two forks. Continued development of the main axis results in a monopodium which gives off