SUMMARY

A wild strain of the multinucleate plasmodial myxomycete Physarum poly-cephalum was isolated in pure culture and grown on a medium consisting of 1 yo (w/v) Tryptone, 1 % (w/v) glucose, 0.15 % (w/v) yeast extract, 0.3 % (w/v) CaCO,, inorganic salts and a small amount of chick embryo extract. The organism may be grown with this medium either as a single large plasmodium on surface culture, or as a suspension of tiny plasmodia in submerged culture. From an initial inoculum of 1 ml. of a %day culture, the average plasmodial yield in a submerged culture was about 80 mg. dry weight/20 ml. medium a t 72 hr. Growth occurred only in the presence of small amounts of an unidentified factor which was present particularly in chick embryo extract and foetal calf serum. An isolate of P. polycephalum was grown continuously on this medium for over four years without an appreciable decrease in growth rate. Under proper conditions a suspension of tiny plasmodia from shaken culture will fuse to form a single large surface plasmodium which exhibits syn-chronous mitosis