The agency wrote, " Excited to see what other species cross" !

该机构写道，“很高兴看到其他物种杂交”！

Why should some species cross with facility and yet produce very sterile hybrids; and other species cross with extreme difficulty, and yet produce fairly fertile hybrids?

为什么有些物种很容易杂交却产生非常不育的杂交种？和其他物种极其困难地杂交， 却产生相当可育的杂交种？