Now, as I have already pointed out, Mendel made no pretence of universal statement: but had he done so, the conclusion, which Professor Weldon here suggests should follow from such a universal statement, is incorrectly drawn. Mendel is concerned with the laws of _transmission of existing characters_, not with _variation_, which he does not discuss. Nevertheless Professor Weldon has some acquaintance with the general fact of variability in certain peas, which he mentions (p. 236), but the bearing of this fact on the difficulty he enuntiates escapes him. _Results of crossing in regard to seed characters: normal and exceptional._ The conditions being the same, the question of the characters of the cross-bred zygotes which we will call _AB_’s depends primarily on the specific nature of the varieties which are crossed to produce them. It is unnecessary to point out that if all _AB_’s are to look alike, both the varieties _A_ and _B_ must be _pure_--not in the common sense of descended, as far as can be traced, through individuals identical with themselves, but pure in the Mendelian sense, that is to say that each must be at that moment producing only homogeneous gametes bearing the same characters _A_ and _B_ respectively. Purity of pedigree in the breeder’s sense is a distinct matter altogether. The length of time--or if preferred--the number of generations through which a character of a variety has remained pure, alters the probability of its _dominance_, i.e. its appearance when a gamete bearing it meets another bearing an antagonistic character, no more, so far as we are yet aware, than the length of time a stable element has been isolated alters the properties of the chemical compound which may be prepared from it.