Gerry/Anthony, please keep talking. Forumists have many & varied interests and are always keen to pick up more knowledge. Just don't tell me that Darwin had problems with his digital camera & laptop 
OK David. Give me a bit of time & I'll produce a short, illustrated account of Goethe's ideas on the morphology of plants which might interest a few forumists.
Goethe’s essay
Metamorphosis of Plants was published in 1790. Although the essay is by no means easy to understand in detail the broad outlines are clear enough. He argues that all the organs along the axis of the plant - style, anthers, petals, sepals, bracts, leaves - are, in some sense, the the same. He seems to suggest that they are all modified leaves. His evidence for this ‘sameness’ is the fact that leaves can be transformed into petals, as in the Tulips illustrated below, or the sexual parts of flowers can be partially or entirely transformed into petals, as in the Primulas illustrated. This will be familiar to many people in double or semi-double flowers. These paintings were prepared for Goethe’s essay.
As far as I am aware this was the first account of what is now known as serial homology, the idea that there is some form of morphological correspondence between different organs of the same individual.
There is a different form of homology which is exhibited between the ‘same’ organs in different individuals, a view again developed in the 18th century. The classic example is the limbs of different vertebrates. So, the forelimbs of birds, bats, horses & humans are said to be homologous - constructed on a common plan - even though they look very different.
In
The Origin of Species, Darwin addresses the question of the second type of homology & claims that it can be explained if it is assumed that all the individuals showing homologous organs are descended from a common ancestor. This is the mainstream - evolutionary - concept of homology (see, e.g., Wikipedia). However, it can be argued that although evolutionary theory explains the
distribution of homologies it does not account for their
existence. Darwin also claims that Goethe’s serial homologies can be explained by descent but his account is, not surprisingly, obscure.
It is only in recent times that the limitations of evolution theory as a
scientific theory have been recognised. In recent years some biologists have begun an attempt to recover the 18th century approach to morphology & to reconsider homology in the context of a general critique of the explanatory power of evolution theory. Rather than turning to
historical explanations of homology in terms of descent they are attempting to develop
scientific explanations in term of how the organs in question develop during the life of the individual. Although this work is at a very early stage, in broad outline the claim is that the development of homologous organs involves modifications of the same basic developmental process. The aim is a
general theory of development which will either replace the theory of evolution as the central theory in biology or stand beside it. This view has been elaborated in a radical fashion to suggest the existence of a hierarchy of homologies & proposes homologies where none have previously been supposed to exist.
For anyone who wishes to pursue these ideas, I recommend the book which I suggested to Anthony -
How The Leopard Lost Its Spots by Brian Goodwin. Although this is intended as a ‘popular’ book I should point out that it does presuppose a fair amount of knowledge of biology.
