The intercalary meristems at the base of leaf blades and sheaths are responsible for leaf expansion. Each leaf is rolled into a tube-like form in its lower portion and unfurls as the blade extends. As new leaves push up from the center of the rolled tube portion of the first leaf, the growth is similar to extension of a telescope. As the first grass leaf is exerted, it extends in length or height through formation and growth of new cells at the base of each leaf blade. Chlorophyll, which develops rapidly in young leaves, gives plants the ability to carry on photosynthesis.
Photosynthesis uses energy from sunlight and carbon dioxide from the air to produce carbohydrates.
However, photosynthesis may not meet the energy demands of the rapidly growing new leaf. Production of the first one to three leaves requires a substantial amount of energy in the form of carbohydrates stored in the crown of the plant. However, as these first leaves fully extend, rapid rates of photosynthesis supply sufficient carbohydrates for growth of other leaves and roots. When severe defoliation occurs, carbohydrates stored in the roots and crowns may be needed to initiate new growth. Leaves have a definite life span, as do tillers.