In regard to the sterility of hybrids in successive generations; though
Gartner was enabled to rear some hybrids, carefully guarding them from a
cross with either pure parent, for six or seven, and in one case for ten
generations, yet he asserts positively that their fertility never
increases, but generally decreases greatly and suddenly. With respect to
this decrease, it may first be noticed that when any deviation in structure
or constitution is common to both parents, this is often transmitted in an
augmented degree to the offspring; and both sexual elements in hybrid
plants are already affected in some degree. But I believe that their
fertility has been diminished in nearly all these cases by an independent
cause, namely, by too close interbreeding. I have made so many experiments
and collected so many facts, showing on the one hand that an occasional
cross with a distinct individual or variety increases the vigour and
fertility of the offspring, and on the other hand that very close
interbreeding lessens their vigour and fertility, that I cannot doubt the
correctness of this conclusion. Hybrids are seldom raised by
experimentalists in great numbers; and as the parent-species, or other
allied hybrids, generally grow in the same garden, the visits of insects
must be carefully prevented during the flowering season: hence hybrids, if
left to themselves, will generally be fertilised during each generation by
pollen from the same flower; and this would probably be injurious to their
fertility, already lessened by their hybrid origin.
Pages:
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453