. Elements of ecology. Ecology. Aquatic Plants 239 illumination close to the surface was excessive and depressed photo- synthesis. The highest rate of oxygen production occurred at 5 m in the middle of the day. No significant amount of photosynthesis occurred at any depth before 0600 in the morning or after 2200 and none below 35 m at Time- Fig. Photosynthesis of a species of phytoplankton (Coscinodiscus) at the indicated depths during the course of the day off Stoke Point, England. (Jenkin, 1937, Copyright, Council of Marine Biological Assoc, of United Kingdom.) If a plant is to
. Elements of ecology. Ecology. Aquatic Plants 239 illumination close to the surface was excessive and depressed photo- synthesis. The highest rate of oxygen production occurred at 5 m in the middle of the day. No significant amount of photosynthesis occurred at any depth before 0600 in the morning or after 2200 and none below 35 m at Time- Fig. Photosynthesis of a species of phytoplankton (Coscinodiscus) at the indicated depths during the course of the day off Stoke Point, England. (Jenkin, 1937, Copyright, Council of Marine Biological Assoc, of United Kingdom.) If a plant is to grow, its photosynthesis during the day must build up enough organic matter to more than make up for the material lost by respiration not only during the day but also during the night. In other words, the crucial value for the continued existence of the plant is the compensation depth for the 24-hour period. This will obviously occur at a shallower depth than the values reported for experiments limited to the middle of the day. The compensation depth for the complete day ranges between 20 and 30 m during the summer in clear coastal water of the temperate oceans. In the winter and in less transparent water the compensation depth occurs cor- respondingly nearer the surface. No constructive growth is possible for diatoms or other pelagic plants below these levels. When we recall that the average depth of the ocean is more than 4000 m, it is. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Clarke, George L. (George Leonard), 1905-. New York, Wiley
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