THE LOCALIZATION AND FREQUENCY OF HAUSTORIA IN COLONIES OF BROWN RUST ON BARLEY LEAVES

Serial sections were taken through colonies of brown rust (Puccinia hordei Otth.) on barley leaf blades. Fungal haustoria occurred in cells of the mesophyll, parenchymatous bundle sheath and epidermis (excluding guard cells) but not within the mestome sheath or vascular bundles. Within a colony, each cell contained 1.2 to 2 haustoria; each colony had about 10⁴ haustoria on a total hyphal length of about 1 m. Surface areas of haustoria and intracellular hyphae were calculated and used to show that all of the hexose needed to sustain fungal growth and respiration could be taken up through either cell type.