Page:Mendel's principles of heredity; a defence.pdf/110

90 and grouping of the elements which exist in the foundation- cells [fertilised ova] of the same in vital interaction.

Even the validity of the law formulated for Pisum requires still to be confirmed, and a repetition of the more important experiments is consequently much to be desired, that, for instance, relating to the composition of the hybrid fertilising cells. A differential [element] may easily escape the single observer, which although at the outset may appear to be unimportant, may yet accumulate to such an extent that it must not be ignored in the total result. Whether the variable hybrids of other plant species observe an entire agreement must also be first decided experimentally. In the meantime we may assume that in material points a difference in principle can scarcely occur, since the unity in the developmental plan of organic life is beyond question.

In conclusion, the experiments carried out by Kölrenter, Gärtner, and others with respect to the transformation of one species into another by artificial fertilisation merit special mention. A special importance has been attached to these experiments, and Gärtner reckons them among "the most difficult of all in hybridisation."

If a species A is to be transformed into a species B, both must be united by fertilisation and the resulting hybrids then be fertilised with the pollen of B; then, out of the various offspring resulting, that form would be selected which stood in nearest relation to B and once more be fertilised with B pollen, and so continuously until finally a form is arrived at which is like B and constant in