Fig. 2. Choline acetyltransferase activity, revealed as a dark precipitate, produced using the method of Burt (Burt, 1970). Mating-competent mt I cell (Ai) and control (Aii). Mating-competent mt II cell (Bi) and control (Bii). Immature cell (Ci) and control (Cii). Non-mating-competent cell (D). The control for the non-mating-competent cell is not shown because the complete absence of staining made it impossible to photograph. Scale bars, 20µm.