An experimental investigation of the form of the temperature structure in the slightly heated plane wake and its relationship to the intermittency and interface structure is described. No evidence is found of periodic interface motion. Furthermore, it is shown that the large scale structures of the interface modulations with wavelengths greater than 10&percent; of the wake width are highly correlated with the large scale temperature structure within the wake and hence that the interface is related primarily to the large scale structure of the flow field.