I took some stem cuttings of my Nepenthes alata a week ago, and now they are starting to turn black. They are in a glass aquarium with plastic wrap over it which receives a few hours of direct sunlight in the morning. There is a tear over the plastic wrap above the plants so there is some air circulation. The Nepenthes cuttings are in long-fibered sphagnum which I water lightly every few days, and were dipped in rooting hormone powder before being planted. The last time I tried to take a cutting the same thing happened.