As the tip of a plant

shoot In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spri ...

grows, new leaves are produced at regular time intervals if temperature is held constant. This time interval is termed the plastochron (or plastochrone). The plastochrone index and the leaf plastochron index are ways of measuring the age of a plant dependent on morphological traits rather than on chronological age. Use of these indices removes differences caused by germination, developmental differences and exponential growth.

Definitions

The spatial pattern of the arrangement of leaves is called

phyllotaxy In botany, phyllotaxis () or phyllotaxy is the arrangement of leaves on a plant stem. Phyllotactic spirals form a distinctive class of patterns in nature. Leaf arrangement The basic arrangements of leaves on a stem are opposite and alternat ...

whereas the time between successive leaf initiation events is called the plastochron and the rate of emergence from the apical bud is the

phyllochron The phyllochron is the intervening period between the sequential emergence of leaves on the main stem of a plant, also rendered as ''leaf appearance−1''. This measurement is used by botanists and agronomists to describe the growth and developme ...

Plastochron ratio

In 1951, F. J. Richards introduced the idea of the plastochron ratio and developed a system of equations to describe mathematically a centric representation using three parameters: plastochron ratio, divergence angle, and the angle of the cone tangential to the apex in the area being considered.Orthostichy, Parastichy and Plastochrone Ratio in a Central Theory of Phyllotaxis
/ref> Emerging phyllodes or leaf variants experience a sudden change from a high

humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...

environment to a more

arid A region is arid when it severely lacks available water, to the extent of hindering or preventing the growth and development of plant and animal life. Regions with arid climates tend to lack vegetation and are called xeric or desertic. Most ar ...

one. There are other changes they encounter such as variations in light level,

photoperiod Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It occurs in plants and animals. Plant photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light a ...

and the gaseous content of the air.

References

{{botany-stub Botany