Plant Tumours Induced by the Combined Action of Wounds and Virus

Abstract

IN an earlier paper¹ various symptoms of wound-tumour disease, such as stunting, vein enlargement, leaf distortion and tumours, were described on several of the numerous hosts of the causal virus Aureogenus magnivena Black². The present communication deals principally with the role of wounds in tumour inception in diseased plants. Fig. 1 illustrates the kind and number of tumours present on the roots of infected sweet clover (Melilotus alba Desr.). A cross-section through a root bearing a tumour (Fig. 2) shows the practically normal portion of the root enclosed within the black line. In this area the parts are, for the most part, regularly arranged. The rest of the section is tumour tissue. It shows several centres of growth, the margins of which are marked by deeply stained meristematic cells with prominent nuclei. The meristematic cells are surrounded by a layer of crushed cells and enclose parenchyma and vascular elements. The xylem is prominent and reveals the highly disorganised condition of the tumour tissue. It may be arranged in whorls or it may be so disorganised that two adjacent xylem elements are disoriented in regard to each other. Affected cells frequently show spherical bodies that stain intensely with safranin. No organisms have been observed in such sections.