@HumphreyRajagopal:02 provided a mathematical treatment of *adaptation* in a tissue, which includes growth and remodelling in the sense of this paper. The authors identified adaptation as perhaps the most important mechanical characteristic of biological tissue. They introduced the notion of evolving natural configurations to model the state of material deposited at different instants in time. The treatment of the growth part of the deformation gradient in this paper bears some resemblance to this idea, although a detailed development has not been pursued here. The focus, instead, is on detailing some aspects of the problem that derive from treatment of the tissue as a porous medium, or as a mixture of interacting species. @PreziosiFarina:2002 developed an extension to the classical Darcy’s Law to incorporate mass exchanges between reacting species. This consideration is relevant to growth problems; however, in our opinion, these issues were subsumed in @growthpaper, upon which this paper is based. Many of the ideas employed here are applicable to tumour growth problems; however, due to our current focus on tendon, we do not include phenomena such as angiogenesis and cell migration [see for example @Brewardetal:2003]. The changes in concentration that occur with growth tend to cause swelling or contraction 