Hugo de Vries gave much importance to the discontinuous variations or saltatory variations and proposed that new species arises by suddenly appearing saltatory variations termed as 'mutation' and not by the accumulation of minor and continuous variations through natural selection.
For Darwin evolution was gradual while Hugo de Vries believed that mutation causes speciation and hence called it saltation i.e. single step large mutation.
He found that several wild and cultivated varieties possessed new minute but inheritable variations.