SURVEY OF INTERVESSEL PIT MEMBRANE-STRUCTURE IN DAPHNE SPECIES

Of 22 species of Daphne surveyed, 19 possessed tori in their intervess el pit membranes. The torus has a circular shape and is centrally-loca ted on the pit membrane. The fibrils of the surrounding margo show a r andom arrangement. In some specimens, the fibrils are obscured by mate rial that impregnates the margo, coats the torus, and lines the cell l umens. The margo has small pores. In those species without tori, the i ntervessel pit membranes, when intact, show randomly-woven fibrils and small pores. Air-dried membranes of these species tend to separate in to two layers along the line of the middle lamella. The presence of a torus is not correlated with evergreen or deciduous habit, but absence of a torus seems to be limited to species of the section Mezereum wit hin the genus Daphne.