Georges Vantongerloo quotes:

One paints from nature not in order to copy, but to express feelings of grandeur.

I see a flower. It gives me a sensation of the beautiful. I wish to paint it. And as soon as I wish to paint it I see the whole subject - flower - changed. It is now an art problem to resolve.

There is no need to express art in terms of nature. It can perfectly well be expressed in terms of geometry and the exact sciences.