Strobili of E. arvense (collected just prior to elongation of axis), subjected to the aerosol-hypochlorite sterilization technique, provided spores for the initiation of aseptic cultures of the gametophyte phase of this spp. Germination of the spores began in light 2 days after sowing on an inorganic medium adjusted to pH 6. The plants became sexually mature during the 3d week, and sex organ production usually continued over a period of 4 mos. The addition of casein hydrolysate (50-200 mg./l.) as a source of organic N shortened the period of germination, increased growth of the thallus, and promoted somewhat earlier production of sex organs. Similar results were produced by the addition of sucrose (1250-20,000 mg./l.). However, casein hydrolysate, sucrose, and combinations of the 2 added to the inorganic medium produced early browning followed by necrosis. Cultures may be maintained over a period of several yrs. on an inorganic medium, with or without low concns. of casein hydrolysate and sucrose, by frequent transfer to fresh medium. Such cultures lose their capacity to produce antheridia and archegonia after 4-6 mos.