Comparative ultrastructure of microhairs in grasses

Ultrastructure of microhairs is described for 17 species of Poaceae, involving four subfamilies and the 'chloridoid', 'panicoid' and 'Enneapogon' morphological types. The plasma membrane invaginations known as partitioning membranes implicated in salt secretion were found in the basal cells of only some of the 'chloridoid type' microhairs. They were absent from 'panicoid type' microhairs, but present in the cap cells of the 'Enneapogon type'. Characteristics common to known secretory tissues, however, were observed in all microhairs studied, implying secretory activity in all the morphological types.