Anatomy of Noncostal Portions of Lamina in the Cyclanthaceae (Monocotyledoneae). II. Regions of Mesophyll, Monomorphic and Dimorphic Ordinary Parenchyma Cells, Mesophyll Fibers, and Parenchyma-Like Dead Cells

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Abstract
The mesophyll within an interridge area has boundary layers and adaxial, abaxial, and somtimes middle regions. Abaxial and middle regions contain spongy mesophyll, whereas the adaxial region is sometimes a palisade mesophyll. The regions of mesophyll are distinguished mostly by the features of parenchyma tissue, e.g., cell size and shape, sizes of intercellular spaces, thickness and differential staining of cell walls, concentration and sometimes size of chloroplasts, and concentration and size of ergastic materials. In all genera the ordinary parenchyma cells contain starch grains, tannin, and crystals; in a few species these cells also exhibit star figures, i.e., stellate inclusions apparently composed of tannin. Between boundary layers, monomorphic ordinary parenchyma cells develop in all species except Dicranopygium macrophyllum and D. schultesii, which have dimorphic ordinary parenchyma cells reminiscent of the dimorphism between sheath cells and nonsheath cells of species outside the Cyclanthaceae, demonstrated to have C4 photosynthesis. Fibers occur in the mesophyll of all Cyclanthaceae but differ quantitatively among various species. Within a species the mesophyll fibers and phloem fibers tend to differ according to cell wall ultrastructure and degree of lignification. Parenchyma-like dead cells occur in all species of the Sphaeradenia group and in several of the Asplundia group. These cells are an extremely important taxonomic character because the ones with strongly birefringent walls occur in all species of the Sphaeradenia group but not in species of the Asplundia group.