Anatomy of Noncostal Portions of Lamina in the Cyclanthaceae (Monocotyledoneae). IV. Veins of Interridge Areas, Expansion Tissue, and Adaxial and Abaxial Ridges

Publisher Website
Google Scholar
Abstract
Interridge areas of cyclanthaceous laminae contain longitudinal veins and commissural veins, which tend to vary from transverse to oblique. Longitudinal veins are normally upright, whereas commissures vary from upright to inverted. In both subfamilies, longitudinal veins are generally of well-defined orders, and up to a given order, the number of veins of an order is twice that of the next-lower order. In longitudinal veins the xylem has tracheary elements, parenchyma cells, and sometimes fibers, whereas the phloem contains sieve elements, companion cells, and fibers. Each large vein exhibits two phloem poles: regions with relatively narrow sieve elements and generally without cells having obviously birefringent walls. In Stelestylis stylaris, phloem poles are not protophloem, despite having narrow elements. Expansion tissue and presumed expansion tissue occur in all species of Carludovicoideae and Cyclanthus bipartitus, respectively. In the Carludovicoideae, expansion tissue may be present in the epidermis, hypodermis, mesophyll between boundary layers, and bundle sheath. The epidermal expansion tissue normally lacks stomata. In this subfamily a band of expansion tissue characteristically develops opposite each adaxial or abaxial ridge and is often more or less bipartite, suggesting that it functions as two laterally adjacent hinges during leaf unfolding. Adaxial and abaxial ridges are mostly associated with one or more longitudinal veins. The main vein of a ridge is normally upright, and additional veins are upright or inverted to various degrees. In interridge areas and ridges, longitudinal veins are normally collateral, but bicollateral, amphivasal, and amphicribal veins may also be present.