Data for stream frequency, F, and drainage density, D, were gathered from five fluvially eroded landscapes in eastern Australia. Analyses of these data and of data published by Maxwell reveal that, in the relation F = jDk for a landscape with a near-uniform environment, the constants j and k vary with order of basin selected for analysis. However, in the relation for a variety of landscapes (environments), k equals 2 irrespective of basin order with which j varies inversely. It is argued that growth models between F and D may be defined only for basins of a given order in a particular landscape. The general implication of this argument is that laws of change through time (growth laws) involving any drainage basin morphometric property that is functionally related to the random development of channel networks may be represented by laws of change over space only where the sampled basins are of the same order (or magnitude) and experience similar environments.