One of the long slender tubes that develop from germinated spores and form the structural parts of the body of a fungus. In many species of fungi, hyphae are divided into sections by cross walls called septa . Each section contains at least one haploid nucleus, and the septa usually have perforations that allow cytoplasm to flow through the hypha. A large mass of hyphae is known as a mycelium , which is the growing form of most fungi. From time to time, hyphae develop reproductive structures that are partitioned from the hypha by holeless septa. In many species, these structures are microscopic; in others, they are visible and large. Mushrooms and shelf fungi are visible reproductive structures of fungi.