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Storage Materials: The axial system of the secondary phloem includes sieve elements which function in the longitudinal conduction of food materials, scle-renchyma cells which have a supporting function, and finally, vertically oriented phloem parenchyma cells which function in the storage materials of food materials. The radial system consists of transversely oriented phloem rays composed of parenchyma cells which function in the transfer and storage materials of food.
Temperatures.—storage materials temperatures range from 30° to 40°F. or more, depending upon the kind of fruit or the variety stored. While temperatures as high as 40° to 50°F. are an aid in retarding the process of ripening and eventual decay, the standard cold-storage materials temperatures of 30° to 32°F. are more effective, since for every 10° rise in centigrade temperature (18°F.) the respiration rate approximately doubles. On the other hand, the temperature must not be lowered to an extent which would injure the tissues. The killing temperature of most fruits is about 29°F. or lower.
Methods.—Three basic methods of storage materials may be distinguished: common or air-cooled storage ; temperature-controlled storage materials; and modi-fied-atmosphere storage materials.
Since the time of Dewar's invention, the use of liquid nitrogen, liquid hydrogen, and other cryogenic, or low-temperature, materials has increased tremendously. The storage materials of cryogenic materials has reached truly gigantic proportions, especially since the advent of satellite-launching vehicles and the use of hydrogen bubble cham-liers in research. For example, liquid hydrogen is often transported and stored in 26,000-gallon (99,000-liter) quantities. |
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