Ein Theil der angeführten Merkmale lässt jedoch eine sichere und scharfe Trennung nicht zu, indem der Unterschied auf einem oft schwierig zu bestimmenden “mehr oder weniger” beruht.
However, part of the traits just listed do not allow for a certain and sharp separation, since the difference often rests on a “more or less” that is often difficult to determine.
separation = Trennung Trennung implies physical and spatial separation, making clear that Mendel is speaking of the actual sorting of seeds and flower parts according to distinctive traits.
more or less = mehr oder weniger A common adjectival or adverbial phrase in German that is used to indicate that an object or process varies by degree only. Mendel places it in quotation marks because he uses it as a noun. Bateson and Sherwood have “of a ‘more or less’ nature”.