Carl Correns, a rediscoverer of Mendel's work, was
Carl Erich Correns was a German botanist and geneticist, who is notable primarily for his independent discovery of the principles of heredity, and for his rediscovery of Gregor Mendel's earlier paper on that subject, which he achieved simultaneously but independently of the botanists Erich Tschermak von Seysenegg and Hugo de Vries, and the agronomist William Jasper Spillman.
So, the correct option is ‘German’.