The physiocrats started a train of thought which was a powerful stimulus to the development of a labour theory of value and surplus value. They did not, however develop such a theory of value themselves. What attention they gave to the problem of exchange-value and price produced results of an altogether different character. Thus while one of their contributions finds its continuation in Smith, Ricardo, and Marx, the other leads to the post-classical supply and demand and utility theories of value.

Chapter III, The Founders Of Political Economy, p. 135 - A History of Economic Thought (1939)