Question

Why would the tips stop growing in jar 2 after we cut them

Answer 1

because tips has meristematic tissue which grows the plant by cell division but after cutting tip of the plant

there is no apical meristematic tissue hence plant can't be grow mpre

Answer 2

Tip of the onion stop growing in jar 2 because we have cut them , apical meristematic tissues are present on the tip of the plant which helps in the growth of the plant.