Isolated Flammulina velutipes fruit bodies were cultured under sterile conditions with the cut base immersed in water or solutions. Stipe elongation on water was only 6% of normal for fruit bodies isolated at 1.1–2.0 cm length, 19% at 5.1–6.0 cm, and the same as for fruit bodies attached to mycelium at 9.1–10.0 cm. Fruit bodies not immersed in water grew less in a saturated atmosphere than those in water. The mycelium must supply other substances than water for normal elongation during about two-thirds of the growth period, and only water thereafter. Isolated fruit bodies fed with filtered glucose, trehalose, sucrose, or mannitol grew better than on water. Maltose and fructose increased elongation only slightly, and sorbose had no effect. Potato extract, yeast extract, and casein hydrolysate gave no or very little growth promotion, but addition of glucose strongly increased growth on the natural extracts compared to glucose alone. Of 21 amino acids added separately to glucose, only asparagine, hydroxyproline, arginine, and to a lesser extent glutamine, stimulated growth of isolated fruit bodies. Growth was not promoted by pure asparagine, glutamine, and serine, or by thiamin or indoleacetic acid. Growth was inhibited by urea, ammonium nitrate, and ammonium tartrate with or without glucose.Growth promoting substances were most effective in young fruit bodies and except for glucose the promotion disappeared in fruit bodies isolated at 6.1–7.0 cm length, which corresponds to the end of the period of rapid elongation. Apical portions of fruit bodies with caps grew better on glucose than whole fruit bodies. Growth of decapitated isolated stipes was not promoted by nutrients.