Polarity and the Induction of Organized Vascular Tissues

Abstract

This work deals with those properties of plant tissues which are responsible for the organization of vascular cells in ordered strands. It is shown that auxin alone is sufficient to cause the differentiation of strands of xylem cells in the parenchyma of pea roots. An artificially induced strand, once it is formed, attracts towards itself newly induced vascular strands, and this attraction results in the union of old and new strands. It is also shown that the application of auxin to natural vascular tissues prevents their being joined by newly induced vascular strands. It is proved that this is dependent on a directional effect and not simply on a local accumulation of auxin. To understand these results, it must be assumed that the polarity in terms of auxin transport is increased during the process of vascular tissue induction. The same polarity, once established, is maintained by the presence of auxin, so that the differentiation of strands perpendicular to the axis of this polarity is prevented. These characteristics of plant tissues concerning auxin transport explain the basic phenomena of the organization of vascular cells in defined and ordered strands.