Procambial Initiation for the Vascular System of Florest of Phragmites (Gramineae-Arundinoideae)

The ontogeny followed in serial transections of spikelet primordia of Phragmites reveals that the three principal procambial traces of the lemma form in isolation in the rachilla node subjacent to the node of the lemma insertion. The median trace is initiated before the main laterals; all three differentiate bidirectionally from their initiation sites. The median trace has an uninterrupted ascent through the internode toward its lemma. Since the ascent of the laterals in the rachilla is variously interrupted by the descending procambial traces, the ascending laterals are redirected toward their original destination by another set of bidirectionally differentiating procambial traces. Such traces are designated "prime" or "capturing" traces. The palea traces also serve as prime traces by displacing the lemma intermediates in the rachilla from the lemma toward the descending stamen traces of the floret. Basipetally differentiating capturing traces like those discovered in Phragmites may occur in panicoid and...