I have harvested some basil seeds and i put them in an envelope in a glass jar. I closed the jar and for the first week it was looking fine. I went on holiday for 4 days and when i came back, the envelope was damp and there was this white, furry thing on the basil seeds. Could anyone help me with what this is?
You almost certainly have mold on your seeds. Apparently the remaining humidity was enough to get a nice mold colony going. If you want to keep your seeds, immediately let them dry out, but there’s no way to tell via the Internet whether the mold has affected only the outer shell of the seeds or also the inside. You could try germinating a small sample and then decide whether it’s worth the effort or not.
In any case, the seeds weren’t dry enough when you put them in the jar, next time make sure that the seeds are fully dry before moving them to sealed jars. I personally prefer small envelopes, but I have to make sure that they are also stored in a dry environment. If your storage area could be or become damp, jars are a good way to keep the seeds dry.