The answer is air.................. lol it said I have to add 20 characters or more so
The stem has more things to transport that's why it has more vascular bundles. The roots only get water from the ground and moving nutrients from the soil to transfer it to the stem. Having more vascular bundles helps the stems to transfer things to leaves and other parts of the plants.
The chlorophyll breaks down making the green disappear and the orange yellow or red become visible
Water reacting with nitrogen gas i think, since it doesn’t actually react
