The Basidia of Exidia Nucleata. I. Ultrastructure

SUMMARY

The nucleus of the basidium of Exidia nucleata is surrounded by an alveolate nuclear envelope. The mitochondria within the basidia have plate-like cristae and are morphologically similar to those reported from other fungi. Also present within the basidia are vacuoles similar to those described in plant cells, oil globules, and two types of unidentified cytoplasmic inclusions. The ectoplast is visible as a single, electron-dense line in good thin sections of KMnO₄-fixed material.

The endoplasmic reticulum is thought to form an extensive, flattened network throughout the cytoplasmic ground substance of the basidium. Continuities between the nuclear envelope and the endoplasmic reticulum and between systems of parallel lamellae and the endoplasmic reticulum are described and illustrated; however, continuities purported to occur in other fungi between the endoplasmic reticulum and other membrane systems and organelles were not observed.

Systems of parallel, double lamellae were noted frequently. Although these systems exhibit certain morphological features of the Golgi apparatus as described in plant and animal cells, sufficient evidence is not available to support a conclusion on their nature and function.

The sub-basidial septa have a structure similar to that reported for the septa of Polyporus versicolor and Pellicularia filamentosa. The pore within the septal pore apparatus becomes occluded, following the collapse of the basidium, by the formation of secondary wall material within the clamp-conection or within the fertile hyphal segment. The septal swellings of occluded pores disintegrate, whereas the cross walls remain intact.