Turing's morphogens, two-factor systems and active transport.

It is shown that Turing’s theory of morphogenesis and Rashevsky’s two-factor models are closely related, both being instances of diffusion-reaction schemes. It is further shown that the morphogenetic character of such schemes invariably gives rise to an apparent active transport, and indeed that it is on this transport that the morphogenetic properties of reaction-diffusion models depends. Some relations between the above and two-factor descriptions of other biological processes are briefly discussed.