Page:Darwinism by Alfred Wallace 1889.djvu/186

164 animals, and presumably from the same cause, too close interbreeding.

Dean Herbert, who carried on experiments with great care and skill for many years, found numerous cases of hybrids which were perfectly fertile inter se. Crinum capense, fertilised by three other species—C. pedunculatum, C. canaliculatum, or C. defixum—all very distinct from it, produced perfectly fertile hybrids; while other species less different in appearance were quite sterile with the same C. capense.

All the species of the genus Hippeastrum produce hybrid offspring which are invariably fertile. Lobelia syphylitica and L. fulgens, two very distinct species, have produced a hybrid which has been named Lobelia speciosa, and which reproduces itself abundantly. Many of the beautiful pelargoniums of our greenhouses are hybrids, such as P. ignescens from a cross between P. citrinodorum and P. fulgidum, which is quite fertile, and has become the parent of innumerable varieties of beautiful plants. All the varied species of Calceolaria, however different in appearance, intermix with the greatest readiness, and the hybrids are all more or less fertile. But the most remarkable case is that of two species of Petunia, of which Dean Herbert says: "It is very remarkable that, although there is a great difference in the form of the flower, especially of the tube, of P. nyctanigenæflora and P. phœnicea the mules between them are not only fertile, but I have found them seed much more freely with me than either parent.… From a pod of the above-mentioned mule, to which no pollen but its own had access, I had a large batch of seedlings in which there was no variability or difference from itself; and it is evident that the mule planted by itself, in a congenial climate, would reproduce itself as a species; at least as much deserving to be so considered as the various Calceolarias of different districts of South America."

Darwin was informed by Mr. C. Noble that he raises stocks for grafting from a hybrid between Rhododendron ponticum and R. catawbiense, and that this hybrid seeds as freely as it is possible to imagine. He adds that horticulturists raise large beds of the same hybrid, and such alone are fairly treated; for, by insect agency, the several individuals are freely