Procambial Initiation for the Vascular System in the Shoot of a Seedling ofSymplocarpus foetidus(Araceae)

Abstract

Every procambial strand was mapped in the apical six disks of insertion comprising the shoot tip of Symplocarpus. Detection of longitudinally discontinuous procambia confirmed that the procambial leaf traces were originally isolated in this monocotyledonous shoot. The initially separate procambia of a nascent leaf trace became linked with a leaf as its leaf trace by further procambial differentiation among the procambial segments and the leaf to be served. The procambial components of the major leaf traces were formed by a succession of five waves within each of the superposed disks of insertion. Space for the additional procambia in the successive waves was made by the expansion growth of each disk. Waves 1-4 made the procambial components of the major leaf traces near the center of the disk, but wave 5 caused the lower end of a major trace to become centrifugal. The first intermediate leaf traces began after the major traces, since only waves 3-5 were involved. The mantle of the meristematic cap was the principal source of new isolated procambia during wave 5. The major and first intermediate traces comprised the inner procambial system. The last intermediate traces comprised the outer or cortical system. The last intermediate traces were made only during wave 5 outside of the meristematic cap. The upper part of a bud trace is like a last intermediate trace, but the lower part may become linked to the inner system by the meristematic cap. The patterns to the initiation of leaf traces discovered in Symplocarpus support a state of procambial initiation in monocotyledonous shoots that involves discontinuous strands.