HYBRIDIZING. 



23 



at least, there are not many well-attested 

 instances of their occurrence. Bentham 

 ascertained that Lapeyrouse's Saxifraga 

 luteopurpurea, and Decandolle's S. atnbi- 

 gua, are only wild accidental hybrids be- 

 tween S. arenaria and calyciflora, being 

 only found where the two latter grow to- 

 gether, and there forming a suite of inter- 

 mediate states between the two. Such 

 genera as Salix, Rosa, Rubus, &c., are pro- 

 bably composed in a great measure of wild 

 hybrids. Gentians have been remarked on 

 European mountains, which have had such 

 an origin. Bentham also mentions Cistus 

 longifolius as being a hybrid between C. 

 monspessiilanus and populifolius, in the 

 woods of Fontfroide, near Narbonne ; and 

 Cistus Ledon is constantly being produced 

 between C. monspessulanus and laurifolius. 

 It is the tendency of hybrid plants, when 

 they produce seeds, to revert to their parent 

 forms, that renders wild hybrids so rarely 

 met with. Herbert, however, mentions the 

 following genera as having produced spon- 

 taneous hybrids : — Ranunculus, Anemone, 

 Hypericum, Scleranthus, Drosera, Poten- 

 tilla, Geum, Medicago, Galium, Centaurea, 

 Stachys, Rhinanthus, Digitalis, Verbascum, 

 Gentiana, Mentha, Quercus, Salix, Narcis- 

 sus, and Crinum. These names appear to 

 be quoted by Herbert on the authority of 

 Schiede. 



Hybrids obtained by fertilizing the pistil 

 of one species by the pollen of another spe- 

 cies, are considered as true mules or h}'- 

 brids ; the result of intermixing two varie- 

 ties of the same species is called a crossbred. 

 It was held that the former was sterile, 

 and incapable of yielding seed ; whilst the 

 others, on the contrary, usually produced 

 fertile seed, which shortly reverted to one 

 or other of the parents, unless again influ- 

 enced by further hybridization. This opi- 

 nion, however, that all vegetable hybrids 

 are sterile, is not found to be tenable, 

 though it is the case to a certain extent. 

 The cause of this sterility is very doubtful ; 

 it has been referred to a want of pollen, but 

 this explanation is unsatisfactory, inasmuch 

 as no appreciable difference of structure in 

 this respect has been detected in those ca- 

 ses which have been made the subject of 

 especial inquiry. Crossbred varieties may 

 certainly be hybridized, but there is in them 



a strong tendency to revert to one of the 

 parents. The progeny of varieties of the 

 same species is in all cases as fertile as the 

 parents. 



Referring to the botanical questions which 

 the hybridizing of plants involves, and rely- 

 ing on numerous well ascertained facts in 

 support of his views. Dr. Herbert considers 

 that genera are the only really natural di- 

 visions among plants, the species and vari- 

 eties of which have all sprung originally 

 from one type ; and that, therefore, there is 

 no difference except in degree — that is, no 

 absolute difference between what are called 

 species and varieties. He further considers 

 that no plants which interbreed can, ac- 

 cording to this vieWj belong to distinct 

 genera, and that any arrangement which 

 separates such plants must be revised ; that 

 discrimination between species and perma- 

 nent varieties of plants is artificial, capri- 

 cious, and insignificant; and, consequently, 

 that the question often raised, whether a 

 wild plant is a new species or a variety of 

 a known species, is a waste of intellect 

 upon a point which does not admit of pre- 

 cise definition. 



The fertilization of plants is supposed to 

 be effected by the emission of tubes of ex- 

 treme tenuity from the grains of pollen 

 when applied to the stigma ; these tubes 

 pass down the style into the ovary, and 

 eventually reach the young ovules, which 

 without this contact are unfertile. The 

 operation, so far as it can be aided by the 

 hybridizer, consists simply in applying the 

 pollen of one plant (which becomes the 

 male parent) to the stigma of the other 

 (which becomes the female parent.) But 

 there are certain conditions which are ne- 

 cessary to fertilization. The flower whose 

 stigma is to be fertilized is to be deprived 

 of its own anthers (if it is an hermaphro- 

 dite flower) before they burst and discharge 

 their pollen, for in this case it would pro- 

 bably be self-impregnated, and then there 

 would be little chance of success, for super- 

 fa3tation, though not held to be impossible 

 in plants any more than in animals, is 

 equally an exception to the general rule, 

 and therefore not likely to occur. The 

 pollen must also be applied at the precise 

 time when the stigma is perfectly developed 

 and covered with its natural mucus, for 



