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Seasonal Growth And Temperature: There are other advantages. In most cases a mixture gives more uniform greenery throughout the season than a single type of grass. This because of seasonal growth and temperature preferences. Bluegrasses thrive in the cool weather of spring and fall and go partially dormant during hot weather. Bent grasses generally make their best growth in hot weather. In dry weather fescues prosper better than other grasses. There are grasses more resistant to being walked upon than others. There are grasses valuable because they germinate and grow quickly, act as "nurses" to the slower-to-get-going kinds and then gradually die out. In the meantime they prevent erosion and help to keep weeds out.
Cave environmental zones may be described in terms either of temperature or of light. The entrance of a cave is a variable-temperature zone, the extent of which depends upon such factors as the size and exposure of the entrance, volume of air and water (if any) entering the cave, and extremes of seasonal temperature. Farther inside the cave, air and water temperature reach nearly complete stability, approximately uniform for the latitude and elevation of the cave; this is the constant-temperature zone. The light zones of a cave are the entrance or twilight zone, and beyond that, the zone of total darkness.
When all of the coats of seeds of some rosaceous forms, such as peach, apple, and hawthorn, are removed, a certain percentage of the embryos, which require cold stratification for normal development, will grow at greenhouse temperatures to form dwarf plants. In such physiological dwarfs, normal growth is readily initiated after exposure of the seedling to a cold period.
Finally, an extreme type of dormancy is shown by seeds of such forms as Convallaria, Smilacina, and Trillium. These require pretreatment at low temperature to break the dormancy of the root, a period at high temperature to permit the root to grow, another period at low temperature to break epicotyl dormancy, and a second period at high temperature to permit the growth of the afterripened epicotyl to form a green shoot.
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