Dicotyledons trees and gymnosperms grow in two main ways, upward by apical growth and outward by cambial growth. As the cambium is forming, fusiform and ray initials are created from the apical shoot cells. From the cambial initials, cells to the inside create the vertical elements of xylem (tracheids, vessels, fibers, parenchyma, etc.), while cells to the outside become phloem. Ray initials produce horizontal elements (rays) \citep{fromm2013cellular}.