Hormones that bind to plasma proteins

Hormones that bind to plasma proteins are insoluble in water meaning that they cannot be transported freely through the blood. Usually those hormones are lipid derivate (cholesterol derivate) such as steroid hormones (estradiol, testosterone). Transport proteins are proteins that hold hormones inactive in systemic circulation and release them when necessary. So, transport proteins are reservoir of hormones within the circulatory system.

it would be c. xylem.