ON DETERMINATION OF PATTERN OF VASCULAR TISSUE IN PEAS

This work is concerned with the rules determining the place of joining of two vascular strands. Auxin can induce the differentiation of vascular tissue, and this fact is used here for an experimental study of the spatial interactions of vascular strands.Differentiated vascular tissue whose source of auxin has been removed attracts newly induced vascular strands. This attraction is expressed in the joining of the new strands to the pre-existing vascular tissue. Differentiated vascular tissue which is well supplied with auxin inhibits rather than attracts the formation of new vascular strands in its vicinity.Experiments on pea apices have extended these results to naturally induced vascular strands. It is shown that when a leaf primordium is damaged at an early age its vascular strands are joined by the strands induced by new leaves, and the contacts may be formed across the leaf gap. The joining of the vascular strands is, therefore, much closer to the leaf than is normal and this is probably due to the reduction in the supply of auxin from the damaged leaf to its vascular traces. It is also shown that when a lateral bud grows its vascular traces join preferentially the vascular system leading to organs which have been removed. These vascular traces of a bud specifically avoid the vascular system of a leaf or a shoot which is still growing and producing auxin.These results are discussed in reference to the relation between the vascular system and phyllotaxis and to the existence of leaf gaps. © 1968 OXFORD UNIVERSITY PRESS.