Seven different grass species were studied to see if they could evolve to tolerate salt. The researchers grew seedlings in solutions with different levels of salt and found that higher salt levels reduced root growth in all species. They then selected plants with longer roots in salty conditions and compared them to unselected plants. The selected plants had longer roots in most species, showing that salt tolerance can evolve in grass species. The ability to tolerate salt varied among species, suggesting that salt tolerance is present but doesn't always evolve in nature.