Ob die veränderlichen Hybriden anderer Pflanzenarten ein ganz übereinstimmendes Ver- halten beobachten, muss gleichfalls erst durch Versuche entschieden werden; indessen dürfte man vermuthen, dass in wichtigen Puncten eine principielle Verschiedenheit nicht vorkommen könne, da die Einheit im Entwicklungsplane des organischen Lebens ausser Frage steht.
Whether the variable hybrids of other plant species observe complete agreement in their behaviour must equally still be decided by experiments; in the meanwhile one might conjecture that in important points a fundamental difference cannot occur, because the unity in the developmental plan of organic life is beyond question.
variable hybrids = veränderlichen Hybriden Mendel refers to Section 10 of his paper, entitled “Experiments on hybrids of other plant species” (p. 32ff.). In that section he was able to explain colour variation exhibiting segregation ratios that differed from the 3:1 ratio he found in his Pisum-experiments on the basis of multifactorial inheritance, and proposed that variability in most cultivars could be explained in similar ways; see p. 37, s. 4.
developmental plan = Entwicklungsplan The manuscript has Entwicklungs-Plane. The term Entwicklungsplan was very common in german morphology and physiology in the nineteenth century, and referred to shared structural, functional and organisational features of groups of organisms. The very phrase Einheit des Entwickelungsplanes appears in Rudolph Wagner, Handwörterbuch der Physiologie, Vol. 4 (Braunschweig: Vieweg, 1853), p. 850, in an article on “generation” (Zeugung). The author (Rudolf Leuckhardt, 1822–1898, a student of Wagner) discusses the development of spermatozoa and claims that it occurs in the same way throughout the animal realm, despite some variation. Rudolph Wagner (1805–1864) taught zoology, anatomy and physiology at the university of Göttingen; on his possible significance for discussions around generation and inheritance in animals, see Vítězslav Orel, Gregor Mendel: The First Geneticist (Oxford: Oxford University Press 1996), p. 33–34. Whether Mendel picked the phrase from this particular source or not, what is striking is that he refers to organisational features that all organisms are supposed to share to explain presumed regularities in the transmission of traits, and not the other way round.