A Three‐dimensional Reconstruction of the Vascular System to the Lodicules, Androecium, and Gynoecium of a Fertile Floret of Panicum Dichotomiflorum (Gramineae)

Abstract

A three‐dimensional reconstruction of a fertile floret stele of Panicum dichotomiflorum approaching anthesis was made by a new technique using superimposition of tracings of 80, 1‐μm thick serial sections, cleared tracing film, and mounting adhesive. From a collateral bundle, which also served as the median trace to the fertile lemma, most of the vascular tissue branched adaxially and horizontally to become the sole vascular supply to the two lodicules, three stamens, and pistil. The xylem branched at a low level to form a broad and long vessel plexus. The phloem branched at a higher level to overlay the vessel plexus on the right and left with an arc of horizontal sieve tubes in a phloem plexus. Those sieve tubes and vessels which rose after branching from the horizontal plexi assumed a more vertical course in the floret stele. Traces to the right and left lodicules arose from the lower abaxial portions of the flanks of the floret stele. Vessels ascended vertically from the xylem plexus and passed through the phloem plexi and joined with the sieve tubes there to exit at the same level and become the right and left lodicule traces. The vascular tissues to the three filament traces arose from different higher levels of the stele. The sieve tubes for the median filament trace arose vertically from the abaxial side between but above the lodicule traces. At higher levels the sieve tubes for the lateral filaments rose from the horizontal arcs of the flanks of the stele and departed it tangentially. The vessels destined to the filament traces arose in the center of the floret stele from adaxial portions of the horizontal plexus, ascended between the arcs of phloem, exited the stele simultaneously above the phloem of the traces, and followed the courses of their respective sieve tubes. The adaxially displaced apex of the floret stele then contained the vascular tissue related to the pistil. All the sieve tubes and vessels of the floret stele were embedded in a matrix of intermediary cells. The peripheral intermediary cells associated with the vessel plexus were xylem transfer cells with pronounced wall ingrowths. At higher levels in the floret stele, intermediary cells in scattered locations near sieve tubes or vessels had less conspicuous wall ingrowths. No preferred orientation of transfer cells with any particular trace was noted.

Vascular System of the Floret of Leersia virginica (Gramineae-Oryzoideae)

“…Microscopic preparation and the construction of a plastic facsimile of the vascular system of one floret was accomplished in the manner previously detailed by Pizzolato (1983bPizzolato ( , 1984Pizzolato ( , 1988 (Fig. Florets with recently extruded stigmas and stamens were excised in the laboratory.…”

“…The distinction rests on the presence of a xylem discontinuity of anomalous tracheary elements (Zee and O 'Brien, 1970) in the floret vascular systems of the studied Festucoideae (Pizzolato, 1983a(Pizzolato, , 1984(Pizzolato, , 1987(Pizzolato, , 1988(Pizzolato, , 1989; O' Brien et al, 1985;Frick and Pizzolato, 1987). The distinction rests on the presence of a xylem discontinuity of anomalous tracheary elements (Zee and O 'Brien, 1970) in the floret vascular systems of the studied Festucoideae (Pizzolato, 1983a(Pizzolato, , 1984(Pizzolato, , 1987(Pizzolato, , 1988(Pizzolato, , 1989; O' Brien et al, 1985;Frick and Pizzolato, 1987).…”