How old are the cuttings? sometimes cuttings will grow leaves before roots come out if the conditions are too warm. you need to see if leaves are still actively growing at the 6 week point. At the two week point, you can raise the jar a bit, and put 3 little spacers between the jar and what it is resting on, to give a crack of ventillation. I actually crack my humididome vents open within a few days of sticking the cuttings, to guard against overheating. Sativa.

Thank you for the most informative response. I suspect that what you say applies to my cuttings, that they may not have grown roots. I propped up the jars slightly, to let gresh air in, and I shall keep them damp, hoping for roots soon.