You should be just fine with that. If you think about it, there are temperature fluctuations all over the room and the reading you are getting is at stat level. I presume, since you are starting the seeds in your basement, you are using lights and that's going to impact heat at plant level anyway. Even fluorescents that close emit enough heat to raise your soil temps.

I have sown it in spring in greenhouses and I can assure you the temperatures they were subjected to were as low as fifties and as high as eighty fluctuating with day and night. They germinated fine.

Oh, thank you! That is just the encouragement I need. I am starting them under lights, and that was worrisome too. I will put them near the floor in the hopes that it's a bit cooler there.

Every seed has an optimum germination temperature. Shown on a graph a variance from that temperature will only make a small change in the germination time, much as a variation in planting depth will in most cases make a slight delay in breaking ground. Al