Hi I am making an experiment with Arabidopsis in MS medium

Below there is a picture of two experiments

I sterilized the seed that I used for both the same day, then I put them at 4°C for 3 days for experiment A and 4 days for experiment B

I prepared the medium for each one in a different day but it has the same composition

Also I used the same growth chamber

Do you have any ideas of what could cause the difference in the growth of roots?

I want to standarize the assay before I start to test any other hormone

Thank you