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Growth Takes: In those species that hibernate at regular intervals, growth takes place during the active period of the animal, and is indicated by rings built up at the edges of each shield. These growth rings give some idea of the age of the animal, but the system fails with older specimens, in which the earlier rings become worn down.
In other species the shields are shed regularly or sporadically so that no growth rings show. With such a specimen, age cannot be determined.
Growth Phase. Three basic factors affect the growth phase of cell populations: (1) the number of organisms involved—the more parent organisms present, the more offspring there can be. (2) During this period most of the organisms reproduce; few are barren. (3) The generation time is constant—that is, the time it takes for each organism to appear, mature, and reproduce is relatively constant throughout the growth period.
Lateral growth in trees frequently begins later than growth in height, but the period of lateral growth is longer. Rates of lateral growth likewise are low at the outset, increasing after a few weeks and then diminishing. In view of the long annual period of lateral growth in trees, deleterious environmental conditions may exercise a pronounced effect on growth. In the wood of trees of temperate regions, narrow and wide growth rings may be observed, marking years characterized by unfavorable and favorable conditions for growth.
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