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But this capacity, as in hybridisation, is by no means absolutely governed by systematic affinity. Although many distinct genera within the same family have been grafted together, in other cases species of the same genus will not take on each other. The pear can be grafted far more readily on the quince, which is ranked as a distinct genus, than on the apple, which is a member of the same genus.
These are potting, watering, and temperatures, after which propagation by means of seeds, cuttings, and grafting, hybridisation, seed saving, &c., and diseases and noxious insects will be treated upon. Soil. The conditions in which plants grow naturally, are what we usually try to imitate for their cultivation artificially.
But this capacity, as in hybridisation, is by no means absolutely governed by systematic affinity. Although many distinct genera within the same family have been grafted together, in other cases species of the same genus will not take on each other. The pear can be grafted far more readily on the quince, which is ranked as a distinct genus, than on the apple, which is a member of the same genus.
As in hybridisation, so with grafting, the capacity is limited by systematic affinity, for no one has been able to graft trees together belonging to quite distinct families; and, on the other hand, closely allied species, and varieties of the same species, can usually, but not invariably, be grafted with ease.
We have no right, they say, to assume, should we find that a variable species can no longer be made to vary in a certain direction, that it has reached the utmost limit to which it might under more favourable conditions or if more time were allowed be made to diverge from the parent type. Hybridisation is not considered by Mr.
Is there any test of a physiological species? The usual answer of physiologists is in the affirmative. It is said that such a test is to be found in the phaenomena of hybridisation in the results of crossing races, as compared with the results of crossing species.
On any parallel of latitude taken in the climatic rather than in the geometric sense the racial composition of the west-European population will be much the same, virtually identical in effect, although always of a hybrid complexion; whereas on any parallel of longitude also in the climatic sense the racial composition will vary progressively, but always within the limits of the same general scheme of hybridisation, the variation being a variation in the proportion in which the several racial elements are present in any given case.
The following conclusions are drawn up chiefly from Gartner's admirable work on the hybridisation of plants. I have taken much pains to ascertain how far they apply to animals, and, considering how scanty our knowledge is in regard to hybrid animals, I have been surprised to find how generally the same rules apply to both kingdoms.
The following rules and conclusions are chiefly drawn up from Gartner's admirable work on the hybridisation of plants. I have taken much pains to ascertain how far the rules apply to animals, and considering how scanty our knowledge is in regard to hybrid animals, I have been surprised to find how generally the same rules apply to both kingdoms.
Nevertheless, double-edged as is the argument from rudimentary organs, there is probably none which has produced a greater effect in promoting the general acceptance of the theory of evolution. The older advocates of evolution sought for the causes of the process exclusively in the influence of varying conditions, such as climate and station, or hybridisation, upon living forms.
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