D, Passage of a nucleus through the sterigma into the basidiospore.
A sexually produced fungal spore borne on a basidium in the fungi known as basidiomycetes. Basidiospores are produced by the union of the nuclei at the tip of a binucleated segment of a hypha. The resulting zygote then divides by meiosis into four haploid nuclei, each of which migrates to the very tip to be released as a basidiospore. A typical mushroom produces billions of basidiospores.