Types of Cell Division. A newly produced jughter cell must synthesize a new set of cell instituents sufficient to equip its daughters for their own cycles of growth and reproduction. Itese constituents must be divided equally to produce normal, well-functioning progeny. This division may be accomplished in a variety of ways.
Growth Cycles.—Longitudinal and lateral (diametral) growth do not proceed continuously, but rather are cyclical phenomena with periods of growth activity alternating with periods of relative inactivity. One of the best illustrations of the periodic nature of growth in large woody stems is to be found in the annual ring pattern which characterizes the wood of trees of temperate regions. It has been suggested recently that even in the apparently ever-growing trees of the tropical rain forest, cambial growth is not a continuous process.
Frequency. The frequency of an electromagnetic wave is equal to the number of cycles per second (Fig. 4). For a radio wave the frequent-may range from a low of about 15,000 cycles pt: second to a high of about 300 billion cycles per second. The unit of cycles per second is named the hertz, Hz (q.v.). Thus, in terms of this unit the radio-frequency spectrum extends from about 15 kilohertz (kHz) to about 300 gigahertz (GHz). However, experiments have been made at lower and higher frequencies for communication purposes. For instance, experiments are being made with laser beams that operate at a frequency greater than 100 trillion Hz.
Types of Cell Division. A newly produced jughter cell must synthesize a new set of cell instituents sufficient to equip its daughters for their own cycles of growth and reproduction. Itese constituents must be divided equally to produce normal, well-functioning progeny. This division may be accomplished in a variety of ways.