How is Darwin's concept of evolution different from that of de Vries?

Explanation

Evolution for Drawin was gradual. It talked about minor heritable variations. It said that Darwinian variations are small and directional.
Evolution for Hugo de vries is based on idea of mutations. He believed that mutation causes evolution. Also according to him mutations are random and directionless. He believed that mutation causes speciation and hence called it saltation (single step large mutation).