IV Conférence Internationale de Génétique (1911)

IS THE LAW OF THE UNIFORMITY OF HYBRIDS OF THE FIRST GENERATION, ABSOLUTE?
M. Gard

SUMMARY

Naudin concluded from his experiments that all the hybrids derived from a cross resemble each other in the first generation. The experiments made by Naudin are, however, not convincing; he did not protect his flowers from insect pollination, and he did not always grow all the seed obtained. In the following account of the experiments made by M. Gard, in hybridizing various species of Cistus, it will be seen that the results of Naudin are not confirmed.

Cistus ladaniferus x C. monspeliensis.— 15 hybrids were obtained, and one plant resembling the seed parent. The former consisted of two types, one of which nearly resembled C. ladaniferus and the other C. monspeliensis.

C. laurifolius x C. monspeliensis.— 12 hybrids were obtained; among these were various intermediate forms.

C. populifolius x C. salvifolius.— 25 hybrids were obtained, and as in the last case, there were various intermediate forms.

C. albidus x C. polymorphus subsp. villosus. 170 hybrids were obtained. Some of these possessed the leaf characters of the seed parent, others those of the male parent, while a third category consisted of intermediate forms.

The reciprocal crosses may give different hybrid forms. C. ladaniferus x C. hirsutus. 12 hybrids were obtained, with lanceolale leaves. From the reciprocal cross, hybrids were obtained, with oval-obtuse leaves.

The reciprocal hybrids may resemble each other in two ways 1st, by their uniformity; 2nd, because they consist of similar, heterogenous types; an example or this occurs in C. albidus x C. polymorphus subsp. villosus, and the reciprocal cross.

The hybrids always possess some of the characters of the parent species; there are many cases in which the hybrids exactly resemble one or other of the parents. For instance, in C. laurifolius x C. ladaniferus fifteen hybrid or intermediate forms were obtained, and four plants which exactly resembled the male parent.

It may be concluded that the first generation from crosses between species of the genus Cistus may be uniform in type, or maybe heterogeneous.