The result would often be greatly retarded by free intercrossing. 查尔斯·达尔文.物种起源.
On this principle nurserymen always prefer saving seed from a large body of plants, as the chance of intercrossing is thus lessened. 查尔斯·达尔文.物种起源.
Intercrossing with the inhabitants of the surrounding districts, will also be thus prevented. 查尔斯·达尔文.物种起源.
Any tendency to modification will also have been checked by intercrossing with the unmodified immigrants, often arriving from the mother-country. 查尔斯·达尔文.物种起源.
In some cases the intercrossing of aboriginally distinct species appears to have played an important part in the origin of our breeds. 查尔斯·达尔文.物种起源.
It would be necessary, in order to prevent the effects of intercrossing, that only a single variety should be turned loose in its new home. 查尔斯·达尔文.物种起源.
Intercrossing will chiefly affect those animals which unite for each birth and wander much, and which do not breed at a very quick rate. 查尔斯·达尔文.物种起源.
These varieties would cross and blend where they met; but to this subject of intercrossing we shall soon have to return. 查尔斯·达尔文.物种起源.