The basidiocarps are recognized by not having an annulus around the stalk of the basidium. A promycelium is formed that consists of a short hypha (equated to a basidium). In summary, meiosis takes place in a diploid basidium. This is where the spore was attached to the basidium. The diploid basidium begins the cycle again. Many basidiospores have an asymmetric shape due to their development on the basidium. An immature basidium is known as a basidiole. "Phellinus tremulae" has spherical spores with four basidiospores per basidium and generative, skeletal hyphae. Following meiosis, mitotic divisions can occur in the basidium. The paired dikaryon in the basidium fuse (i.e. karyogamy takes place). Generation of a four-celled basidium occurs, leading to haploid basidiospores that create sporidia. The basidium may be stalked or sessile. The basidium directly penetrate the cuticle and epidermis. These spores are passively released and may remain on the basidium in chains, unless disturbed. Often such species form only two spores per basidium, but that too varies.