Let's start with the fact the the phloem of a plant is a special tissue that mainly transports food sources for the plant. one of the products it transports is various sugars - more commonly known as sap. the higher the concentration of sugars, the lower the concentration of water. in that case, the plant slows down on sugar making as it has a surplus, and once the sugars dilute within the sap and water's been taken in, the plant goes back to sugar making.
