Many species of fungi form a mycelium, an indeterminate system of protoplasm-filled, apically extending, branching tubes (hyphae). At the macroscopic level, mycelia produce organisational patterns that are found in many other indeterminate systems (e.g. nervous and vascular systems). Therefore they provide an experimentally and observationally accessible model system for investigating the dynamic origins of phenotypic patterns in such systems. Moreover, mycelial fungi form a vital link in the ecosystem allowing for the redistribution and reutilisation of nutrients and minerals over a far wider spatial domain than would be possible without their presence.In vivothese networks grow and function in heterogeneous environments and therefore to gain any true understanding of their form and function such heterogeneity must be taken into account. In this paper we develop a model based on a system of partial differential equations for the interaction of the fungal mycelium with a heterogeneous environment. Using this model we are able to test the hypothesis that mycelia react to their environment in a global manner and by close comparison with experimental results, we are also able to highlight two specific mechanisms in this global response which are central to the macroscopic distribution of biomass: uptake of nutrients in excess of local needs and subsequent internal redistribution (translocation) of this excess.