On the 7th day after soaking, 10-mm sections were cut from the third stem internode immediately below apical hooks which had just reached a 900 angle. Such sections were randomized by floating on water in a large Petri dish and 10 were later added to 20 ml of solution in a 10-cm Petri dish for each test. The sections were incubated in a basal medium composed of 1.5% sucrose, 5 mm KH2PO,, pH 5.5, and 50 jM CoCl, with emulsion stabilizer as noted below. When 1.8 /-M IAA and 0.3 /M GA are added, this medium supports maximal extension of pea stem sections under our conditions. After 20 to 24 hr of slow rotation on a shaker at 25 C in the dark room, the length of the sections was measured to the nearest tenth of a millimeter. Average lengths and standard deviations obtained for each dish were later correctly combined via addition of sum of the squares to obtain the average values in the tables which were usually based on three assays of each substance.Emulsification.