Biggins, J. D.; D'Souza, J. C. - In: Stochastic Processes and their Applications 48 (1993) 2, pp. 237-249
A natural sufficient condition is given for a Galton-Watson process in a varying environment to have a single rate of growth that obtains throughout the survival set of the process. In the homogeneous process the growth rate is provided by the usual Seneta-Heyde norming.