zygote requires two cells of different mating types (heterothallic). Plasmodium The second trophic phase begins with the development of the plasmodium. The multinucleated organism now absorbs via phagocytosis as many nutrients as possible. These are bacteria, protists, dissolved substances, moulds, higher fungi and small particles of organic material. This enables the cell to undergo enormous growth. The nucleus divides multiple times, and the cell soon becomes visible to the naked eye and usually has a surface area – depending on the species – up to one square metre; however, in 1987 one artificially cultivated cell of Physarum polycephalum attained a surface area of 5.5 sq m. Myxogastria species have numerous nuclei in their trophic plasmodium phase; the small, non-veined proto-plasmodia have between 8–100 nuclei, while large, veined meshworks have between 100 and 10 million nuclei. All of these remain part of a single cell, which has a viscous, slimy consistency, and may be transparent, white, or brightly coloured in orange, yellow, or pink. The cell has chemotactic and negative phototactic capabilities in this phase, meaning that it is able to move towards nutrients and away from dangerous substances and light. The movements originate in the grainy cytoplasm, which streams by pulsation in one direction within the cell. In this way the cell reaches a speed of up to 1000 μm per second – the speed in plant cells is 2–78 μm per second. A resting state, the so-called sclerotium, may occur in this phase. The sclerotium is a hardened, resistant form composed of numerous "macrocysts", which enable the myxogastria to survive in adverse conditions, for example during winter or dry periods, in this phase. Fructification Mature plasmodia can produce fruit bodies under appropriate circumstances, the exact triggers for this process are unknown. According to laboratory researchers, changes in humidity, temperature or pH value as well as starvation periods were thought to be the triggers in some species. The plasmodia abandon their nutrient intake and crawl, attracted by light – a positive phototaxis – towards a dry, light area, to get an optimal spread of the spores. Once the fructification begins, it cannot be stopped. If disturbances occur, malformed spore-bearing fruit bodies are often produced. The plasmodium or parts of the fruit bodies can be smaller than one millimetre, in extreme cases they are up to a square metre and weigh up to (Brefeldia maxima). Their shape is often pediculated or