Short Notes:

When a plant first emerges from the ground, a single shoot, perhaps with one or two juvenile leaves, begins growing toward the sun. The shoot grows taller at its tip and wider at its base, and all the while new leaves sprout from the growing stem. A little nodule - a bud - soon appears on the stem, and suddenly the bud becomes a new stem branching off from the first one. Now there are two stems sprouting leaves; then more buds appear, and more stems. From a tiny seed a mighty oak is growing.

At the same time that a stem is growing longer at its tip, the inside of the new stem is also changing. Cells grow larger and take on specific roles.

Some cells, for example, die, become hollow, and form the xylem, the tissue that transports water from the roots to the rest of the plant. Others produce a coat of lignin, a stiff material that gives the stem its strength. There are changes, too, within the leaf. The outer layer of cells, called the epidermis, develops a protective coating that keeps the leaf from losing water. Other cells on the surface guard the pores that admit carbon dioxide and allow oxygen to escape. Most cells beneath the surface produce chlorophyll and carry out photosynthesis. The remaining cells form the veins that transport food from the leaves to the rest of the plants.