Procambial Initiation in Pistils of Phragmites (Arundinoideae, Gramineae)

Serial transections of developing pistils of Phragmites show stages of procambial initiation. Initially the pistil is a residual meristem isolated by intervening parenchyma from procambia elsewhere in the floret. Procambia of the placental bundle and the two stylar bundles simultaneously differentiate from the proximal portion of the residual meristem. As these three procambial traces differentiate acropetally, the procambial pistil prong develops to link them, by differentiating basipetally through the parenchyma of the rachilla, with the other procambia of the floret. The stylar procambia differentiate acropetally into the styles, and the placental bundle differentiates more slowly into the placenta of the ovule. This pattern of procambial development in Phragmites of the subfamily Arundinoideae, which is quite different from that in the subfamily Pooideae, may be a characteristic of the other grass subfamilies as well.