Einer wesentlichen Verschiedenheit begegnen wir bei jenen Hybriden, welche in ihren Nachkommen constant bleiben und sich eben so wie die reinen Arten fortpflanzen.
We encounter an essential difference in those hybrids which remain constant in their descendants and propagate themselves in the same way as pure species.
essential difference = wesentlichen Verschiedenheit Mendel refers to those hybrids whose progeny “remain perfectly similar”, which he mentioned on p. 38, s. 10 already. They differ “essentially” from the cases discussed in the preceding, because their development does not happen “according to the law valid for Pisum” (see p. 39, s. 5).
constant = constant See p. 5, s. 5.
pure species = reine Arten Sherwood has “pure strains”, we follow Bateson; see p. 24, s. 6. .