Horticulture Principles and Practices

them to maturity. The major processes include photosynthesis, respiration, transpiration,
and translocation. Photosynthesis is the process by which green plants manufacture
food from water and nutrients absorbed from the soil and light energy. Photosynthates
are translocated to other parts of the plant where, through the process of respiration, the
energy locked up in the food is released for use by the plants. Gaseous exchange
between the plant and its environment occurs through pores in the leaves called stomata.
Plants lose moisture by the process of transpiration. Plant development and growth occur
in phases described by a sigmoid curve—a rapid logarithmic growth phase, followed
by a decreasing growth phase, and then a steady growth phase. Plants have two
general phases in their life cycles—a vegetative phase and a reproductive phase. Based
on the duration of the life cycle, plants can be categorized into annuals, biennials, perennials,
and monocarps. In flowering plants, a reproductive phase follows a vegetative
phase. Flowers are produced and eventually become pollinated and fertilized to produce
seed and fruit. When plants are subject to adverse conditions in the environment, they
develop a variety of physiological disorders such as wilting, drying, cracking, and abnormal
growth.
REFERENCES AND SUGGESTED READING
Galston, A. W. 1980. Life of the green plant, 3d ed. Englewood Cliffs, N.J.: Prentice
Hall.
Nicklel, L. G. 1982. Plant growth regulators: Agricultural uses. New York: Springer-
Verlag.
Noggle, G., and G. F. Fritz. 1983. Introductory plant physiology, 2d ed. Englewood
Cliffs, N.J.: Prentice Hall.
Wareing, P. F., and I. D. J. Phillips. 1985. Growth and differentiation in plants.
New York: Pergamon Press.
More, R., and W. D. Clark. 1995. Botany: Form and function. Dubuque, Iowa:
Wm. C. Brown Publishers.
Raven, P. H., R. F. Evert, and S. E. Eichhorn. 1992. Biology of plants, 5th ed.
New York: Worth Publishers.
Photosynthesis
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html
Photosynthesis
http://www.biology.arizona.edu/biochemistry/problem_sets/photosynthesis_l/
photosynthesis_l.html
PRACTICAL EXPERIENCE
1. Translocation. Obtain a young tree (about a year old) and girdle the midsection by
carefully removing the bark and making sure to scrape away the phloem layer completely.
Maintain the plant under proper growth conditions in which it will be able
to photosynthesize adequately. After some time, the upper edge of the girdle should
begin to swell from accumulation of photosynthates being translocated down to
other parts of the plant from the leaf.
2. Growth regulators. Cytokinins and gibberellins stimulate plant growth, and abscisic
acid is an inhibitor. Commercial growth regulators are available. Plant geraniums in
pots and divide the pots into two groups, each containing plants of equal size. To one
set apply a growth regulator (e.g., Cycocel) and leave the other as a control.You may
also apply various concentrations of the hormone. Observe the changes in growth
after a period by comparing hormone-treated plants with controls.
Practical Experience 183