Epsilon Open Archive

Abstract

Peridermium pini growing in the green, parenchymatous cortex of a young tree of pine (Pinus sylvestris) has been studied by electron microscopy. The extensively branched septate hyphae are spread in the intercellular spaces and in the middle part of walls separating contiguous host cells. The hyphal cells are uninucleate. The septa are simple and perforate. The septal pore is occluded by a Woronin body. This organization of the septum is similar to that of some Ascomycetes, as is the occurrence of a centriolar plaque on the nucleaer envelope. P. pini has in addition a structural configuration characteristic for rust fungi, namely an approximately hemispherical pore apparatus bordered by a layer of microbodies. The sac-like haustorium is separated from its extracellular mother cell by a cross-wall, situated in the short neck region. At the place of penetration, the host wall forms a papilla-shaped collar. Almost one third of the haustoria observed becomes encased by an extensively proliferating collar. A few per cent of the haustoria become necrotic after having entered host cells. The attacked parenchyma cells, which may each contain several haustoria, have generally an affected plasmalemma and more or less degenerated chloroplasts.