Page:Mendel's principles of heredity; a defence.pdf/32

 {|
 * rowspan=2 |3 ||rowspan=2 | ||| 1 ||Ab class may produce either all Ab's,
 * 2 ||or both Abs and abs.
 * rowspan=5 |9 ||rowspan=5 | ||| 1 || AB class may produce either all AB's,
 * 2 ||or both ABs and Abs,
 * 2 ||or both ABs and aBs,
 * 4 ||or all four possible classes again, namely,
 * ||ABs, Abs, aBs, and abs,
 * }
 * 2 ||or both ABs and Abs,
 * 2 ||or both ABs and aBs,
 * 4 ||or all four possible classes again, namely,
 * ||ABs, Abs, aBs, and abs,
 * }
 * 4 ||or all four possible classes again, namely,
 * ||ABs, Abs, aBs, and abs,
 * }
 * }

and the average number of members of each class will approach the ratio 1:3:3:9 as indicated above.

The details of these experiments and of others like them made with three pairs of differentiating characters are all set out in Mendel's memoir.

Professor de Vries has worked at the same problem in some dozen species belonging to several genera, using pairs of varieties characterised by a great number of characters: for instance, colour of flowers, stems, or fruits, hairiness, length of style, and so forth. He states that in all these cases Mendel's principles are followed.

The numbers with which Mendel worked, though large, were not large enough to give really smooth results ; but with a few rather marked exceptions the observations are remarkably consistent, and the approximation to the numbers demanded by the law is greatest in those cases where the largest numbers were used. When we consider, besides, that and  announce definite confirmation in the case of Pisum, and de Vries adds the evidence of his long series of observations on other species and orders, there can be no doubt that Mendel's law is a substantial