在动物杂交物种上，我们也发现了同样的现象。
在植物方面，我们已有确实的证据，表明杂交物种的不育性一定是由于某种原理而起。
With plants we have conclusive evidence that the sterility of crossed species must be due to some principle.
既然它们能够而且确实可以成功杂交繁殖，它们就不能被归为不同的物种。
Since they can and do successfully inter-breed, they cannot be classed as different species.
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