Depending how tall they were when you took them, I'd cut the brown off and dip em again in my rooting hormone.. It's very likely that you should scrap them, but my last batch of clones a few weeks ago took longer than 2 weeks to come thru because their mother had been in bloom for 2 weeks before I took the clones (stress).. Not all of them pulled thru, but sometimes its worth going the extra mile... Add some pics.. Are they in rockwool, root riots, peat pucks or what.. ? I found that if the medium of too wet then I get rotten stems, ensure grow cubes are damp and not ringing wet.. safe !!