The fine structure of septa and haustoria of Cronartium quercuum formae speciales fusiforme on Quercus rubra

Greenhouse plants of the northern red oak, Quercus rubra, were inoculated with aeciospores of Cronartium quercuum f. sp. fusiforme collected from the alternate host, Pinus elliottii var. elliottii, the widely cultivated slash pine. Infected leaf tissue of oak was fixed and embedded for ultrastructural study. This report consists of observations on the fine structure of septa and haustoria of the rust fungus. Both primary and secondary septa were found. Primary septa are essentially the same as those reported for other rust fungi; there is a single pore that may be plugged by an electron-dense substance and which is surrounded by an organelle-free zone encircled by microbodies. Haustoria of C. quercuum f. sp. fusiforme differ from other rust fungi in the structure of the collar which is continuous with the extrahaustorial matrix.