An anastomosis is a 'bridge' between two adjacent hyphae.
Anastomosing is a very important and often undervalued capability of fungal hyphal systems. The bridge fuses completely with the two hyphal elements and is open at both ends to permit more or less unrestricted protoplasmic flow between the hyphal parts. In the photomicrograph the hyphal grid formed by multiple anastomoses appears two dimensional because this 'demonstration' has been 'engineered ' on a glass slide.
In nature, hyphal anastomoses (plural) form three dimensional grids in soil, wood, debris, foodstuffs or whatever. Remember that the cross walls of a hypha are perforated by a central pore through which protoplasm streams at up to 12 cm an hour (pretty fast really !!) so that there is complete protoplasmic continuity amongst all parts of a hyphal system. The advantages of the grid are similar to electrical power grids. If any part of the hyphal system is damaged or disturbed (e.g. eaten by mites, springtails, insects etc. then the damaged part of the system can be by-passed without the entire system being compromised. New anastomoses can be developed for repair purposes.
Anastomoses are also important to introduce 'new' genetic material into a hyphal system. If the two adjacent hyphae are of the same species but different strains then in some groups (particularly Deuteromycota ) anastomoses will take place between hyphae of the two strains and nuclei from one system can migrate through the bridge to the second system. In this way a monocaryon (one type of nucleus present ) becomes a heterocaryon (more than one type of nucleus) and the fungus can use the DNA cabability of both nucler types to advantage. When two types of nuclei are present it can also be called a dikaryon but this term is often used more specifically for the hyphae of the Basidiomycota where each cell contains two nuclei one of each type. In a heterocaryon of some of the Deuteromycota each cell may contain a number of nuclei. Some of one type some of the other and the nuclear ratio needn't be 1:1. Also in the Deuteromycota you can introduce another nuclear type into the system so that we now have a three nuclear type hyphae (tricaryon). The ratio of all three nuclei can shift according to demand. I once showed in a heterocaryon of Penicillium expansum that the two nuclear types were in the ratio of approximately 10:1! How did I do that?
In fungi the hyphae are microscopic and more or less undifferentiated (no tissue development) yet can produce comparatively massive fruitbodies like mushrooms. Large fleshy umbrella-shaped heads are supported sometimes on relatively slender stalks. The stalks are formed from closely packed, vertically oriented hyphae. Short anastomoses form crosswise between adjacent vertical hyphae and 'brace' the vertical 'struts'. Just like framing a house!
Specialized Structural Modifications
nematode-trapping devices etc. Under Construction - more later -