F pumila is a clinging vine that eventually can developed a specialized adhesive pad from adventitious roots that grow along the length of the vine. These pads secrete a sticky compound that allows the plant to cling to almost any material. The adventitious roots first form in pairs at internodes on young stems. As they divide, the root hairs stick together forming the adhesive pad. If the pad doesn't come in contact with a substrate it eventually dries up. Key to you, is the fact that if they touch moist soil while they are young, they (the roots) tend to morph to a terrestrial form, which makes them one of the easiest of plants to root.

Be patient. You're on people time and the plant is on plant time ...... and stop tugging on it to see if it's rooted! ;-)

Al

What Al said.

Will also add that, for many plants, soil warmth is beneficial for cuttings to root. Considering the time of year, perhaps your dwelling is cool enough to slow down the rooting process? Keep the cutting(s) OUT of direct sunlight and in a warm brightly lit area. (Since the cuttings have no roots, being in direct sunlight can cause the cuttings to dry out too quickly before roots have a chance to develop.) Typically you will know rooting has occurred when you see new leaves being produced.