The body thus formed ment of is called the embryo, and this develops into the adult Primary plant, not by continued growth of all its parts as in an animal, but by localization of the regions of cell-division and growth, such a localized region being called a growing-point.
On germination of the seed the radicle first grows out, increasing in size as a whole, and soon adding to its tissues by cell division at its apical growing-point.
Further growth in length of the stem is thenceforward confined to the apical growing point situated between the cotyledons.
In other cases this growing-point becomes active at once, there being little or no elongation of the hypocotyl and tbe cotyledon or cotyledons remaining in the seed.
This is known as exogenous branch-formation In the root, on the other hand, the origin of branches is endogenous The cells of the pericycle, usually opposite a protoxylem strand divide tangentially and give rise to a new growing-point.
