Changes in the Shoot Apex during the Early Development of the Fern Marsilea vestita

Abstract

Marsilea is an aquatic fern which can be grown in sterile culture and which passes through a juvenile phase before reaching adulthood. It is therefore an ideal plant to use in examining the events at the shoot apex which lead up to the production of juvenile and, later, adult leaves. Allsopp¹ has suggested that in Marsilea a small apical meristem initiates primordia with a relatively limited capacity for development, and Cutter² states in her review: “It is thus held that there is an important correlation between the size of the shoot apex and the extent of development of the leaf primordia to which it gives rise, leaf primordia formed on a large apex being capable of developing into adult leaves, whereas those formed on a small apex are considered to have only a limited capacity for growth and development. Apical regions of well-nourished sporelings with adult leaves are seen by inspection to be larger than those of less-well-developed sporelings with juvenile leaves, but no detailed study of changes in size of the apex in Marsilea has yet been undertaken”. The object of this communication is to find out whether there is any correlation between the size of the shoot apex and the production of juvenile or adult leaves.