THE BASIDIA OF EXIDIA NUCLEATA. II. DEVELOPMENT

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Abstract
The basidia of Exidia nucleate, were studied by light and electron microscopy. The basidium arises from a basal clamp‐connection as a subcylindrical, dikaryotic structure but soon becomes sphaeropedunculate. Mitochondria, endoplasmic reticulum, and compact lamellar systems are more abundant and more evenly dispersed in diploid probasidia than in dikaryotic probasidia, whereas vacuoles in the apical regions are larger in dikaryotic probasidia. Oil globules are few or absent in the earlier stages but increase in size and number throughout basidial development. Karyogamy results in a diploid nucleus approximately twice the volume of haploid nuclei. Although indications were noted of reorganization of the nuclear envelope during the terminal stages of reduction division, available evidence does not suggest a prolonged loss of the nuclear envelope during division. Internal wall formation is centripetal, at least in those stages observed. In areas of active wall formation, a conspicuous zone devoid of mitochondria, oil globules, and endoplasmic reticulum was noted consistently. The circumscribing wall of a hypobasidial segment is composed of 2 lamellae of contrasting electron‐density and is separated from the walls of adjacent hypobasidial segments and the wall delimiting the enucleate stalk by a median electron‐transparent lamella. Although extensive vacuolation occurs in the hypobasidial segments as the nuclei and most of the cytoplasm pass through the epibasidia into the basidiospores, evidence of active nuclear migration was observed. Each basidiospore contains a nucleus, mitochondria, endoplasmic reticulum, and numerous oil globules.
Funding Information
  • National Science Foundation (G–14126, GB–517, G–21796)