PARAVENOUS MESOPHYLL IN CALLIANDRA-TWEEDII AND C-EMARGINATA (LEGUMINOSAE, MIMOSOIDEAE)

Paraveinal mesophyll (PVM) in Leguminosae, subfamily Mimosoideae, was first reported in 1894 but never described in detail before now. We cl eared, and sectioned in resin, leaflets of Calliandra tweedii and C. e marginata (Tribe Ingeae). Lamina anatomy in both species is very simil ar: one palisade layer, two to three spongy layers, and the horizontal veinal network with its interconnected PVM in between. PVM is a unist ratose cellular lacework extending between veins and attached medianly along each flank of all veins. PVM cells have a normal complement of typical chloroplasts similar to other mesophyll cells. Most veins are ensheathed by fibers except for an extended lateral slit along each fl ank where the PVM is attached; a parenchymatous bundle sheath is there fore lacking. All vein endings lack phloem, although the tracheary ele ments of some vein endings are flanked by one or two long, slender, se emingly undifferentiated cells. Occasional small gaps occur between th e PVM cell wall and adjacent tracheary elements, which expose xylem di rectly to mesophyll intercellular space. PVM anatomy of Calliandra, in cluding its physical relationship to the various vein orders, differs in some important respects from PVM of the few other leguminous and no nleguminous species studied anatomically in any detail.