Stems arise from buds that develop on the protonema surface. He directly observed the germination of spores and formation of the protonema. The tip continues to divide new cells, which produces a thalloid protonema. A germinated spore develops into a protonema (a branched, threadlike structure). The gametophyte stage starts with the haploid spore, which then germinates into thalloid protonema. After further development, the later stage of protonema, caulonema, develops. Moss spores germinate to form an algae-like filamentous structure called the protonema. As stems grow, they develop their own rhizoids and become independent of the protonema. The germ tube develops into the hypha, protonema or thallus of the gametophyte. Rhizoids grow down from the protonema and penetrate the substrate. Begins with the haploid spores that gives rise to protonema, and eventually producing the gametophyte. Instead, they regenerate directly into the filamentous protonema, mimicking a germinating moss spore. This protonema develops buds which grow to become either a male or female gametophyte. Protonema is a combination of chloronema, caulonema and rhizoids. In either case, the protonema is a transitory stage in the life of a hornwort.