Answer: This would be very unusual! It may be that they are taking a day to unfurl any foliage, or, if you used a potting mix other than fresh sterile soilless mix, it might be a grass sprouting? The only other thing I can think of that could cause that kind of appearance is slug damage, but in that case you would see the slime trails inside the dome. In any case, if it is the marigolds coming up, you will want to remove or at least prop open the lid from now on to allow for air circulation and avoid overheating the container.
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