This is another diagram (cf. p. 30, s. 1), not a mathematical formula. The mathematical operators / and + make little sense when read literally, perhaps with the exception that A/A and a/a would equal 1, i.e. constitute some “unit”. To represent the joining of two gametes as a “fraction” also makes little biological sense: in no way do pollen and germ cells “divide each other” when joining to form a zygote (while one might say with some justification that they add, or form a product). At the most, one might say that they enter a “relationship” or “proportion” (Verhältniss; see p. 3, s. 8). Be that as it may, the main purpose of this diagram is simply to represent the different combinations that germ- and pollen cells enter through fertilisation. It is notable, that, in this context, Mendel clearly represents like factors entering the products of fertilisation as discrete entities that retain there individuality, whereas he otherwise always represents them as units in his notation system; see p. 17, s. 6, and p. 30, s. 7, for further discussion.