Charles Darwin's Natural Selection: Being the Second Part of His Big Species Book (1856-1858) pp. 395-396
Ed. by R. C. Stauffer

Mirabilis Hybrids

5 Compare Nova Acta Petropol. for 1795, p. 324. and 1797 p. 373, 375.

... Kölreuter5 found that the hybrid Mirabilis jalapa-longiflora fertilised by the pure M. longiflora, produced plants more sterile than their hybrid mother. These plants (which were 3/4 M. longiflora & 1/4 M. jalapa) produced with their own pollen seven seedlings, of which some were quite sterile. But three of the seven produced altogether 15 plants which were very sterile. But one of the fifteen produced nine seedlings; the seeds of these nine seedlings seemed nearly worthless. Here then we have a high degree of sterility continued down to the gr-gr-grandchildren (self-fertilised in each generation) of a hybrid which was fertilised by one of its own pure parents.

1 Gaertner Bastardz. s. 418-421.
2 Gaertner Bastardz. s. 439.
3 Gaertner Bastardz. s. 553.

In the cases just given, the first hybrid had been fertilised, either in one or in all the succeeding generations by the pollen of one of the two parent species. In hybrids fertilised from the first by their own pollen, Gaertner repeatedly states that he has never known the fertility to increase in the successive generations, even in the case of the most fertile hybrids; but he has often known it to decrease; so that in a late generation the hybrid could not he fertilised even by the pollen of either pure ancestral species.1 In the successive generations of self-fertilised hybrids, occasionally a seedling is produced extremely like one of its pure ancestral species; but such seedlings are not more, generally less, fertile than the first hybrid.2 Gaertner gives a full account of the successive generations of Dianthus armeria-deltoides: this hybrid yielded seed for ten generations; having sown itself in his garden for the first six or eight; at each generation it yielded less & less seed, & at the tenth its fertility was quite lost.3

4 No record is given of the fertility of these three last plants. Compare
Nova Acta Petropol. 1795. p. 332. & 1797. p. 373, 381, 392, & 403.

I will abstract two analogous cases from Kölreuter: Two hybrid plants of Mirabilis jalapa-longiflora, self-fertilised produced 16 seedlings (grandchildren of the two pure species), most of which were very sterile; but one produced nine seedlings. Of these nine, four were slightly fertile & altogether yielded ten plants, which were excessively sterile, only one having produced anything, namely three seedlings. These three were the gr-gr-gr-grandchildren of the two pure species.4

5 Nova Acta, 1793. p. 394; 1795 p. 316; 1797, p. 383-389.

Kölreuter found the cross between Mirabilis jalapa & M. dichotoma, nearly as fertile as the pure species so that he says he should have doubted whether the parents ought to have been considered as distinct species, had it not been for the portentous stature of the hybrids. One of the hybrids thus raised, & self-fertilised produced 28 seedlings, of which 14 were more fertile than their hybrid parent & some of them even more fertile than their pure grandmother, M. jalapa; but the remaining 14 were considerably less fertile, Kölreuter then took eight of the most fertile of these 28 hybrids, & raised from them 34 seedlings: of the 34, (which were gr-grandchildren of the two pure species) only one produced an abundance of seed, & nine were excessively sterile. So that we have seen in some of the hybrids of the second generation a marked increase of fertility (in opposition to Gaertner's statement), but found in all except one of the third generation a high degree of sterility.5

Gaertner: Versuche und Beobachtungen über die Bastarderzeugung im Pflanzenreich. (1849)

Mirabilis bibliography