A close look at the marigold seedlings show that a couple of them are tricotyledon (three leaves) rather than the usual dicotyledon (two leaves) a bit of a rarity as it’s a recessive gene trait. See the one in the bottom left of the above picture.
I see on the internet (and everything you read on the internet is true) that tomatoes have a 1 in 40,000 chance of being tricotyledon, but it appears it’s a little more common with marigolds as I have two in my tray of 23 seedlings.
I’m not sure if this gives these plants any advantage, or if the supporting root system is bigger as well resulting in faster growing or bigger plants but it will be interesting to watch them grow compared to their neighbours.
One another note there’s a tray full of tomato seedlings; Golden Sunrise and Black Russian, sown 5 days ago, that started sprouting only yesterday. This is 5 days after sowing, it really does amaze me how quick some of these seedlings grow: