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Records of All Stations and of a Tank of Sea-Water

water, cc, photosynthesis, table and temperature

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RECORDS OF ALL STATIONS AND OF A TANK OF SEA-WATER.

Table 4 gives the determinations of the surface water at station A (fig. 4) on the eastern side of Loggerhead Key for the month of July 1917, and table 5 gives similar data of a tank of sea-water 4 by 6 by 4 feet for July 23-24. The unit of tension is one ten-thousandth of a normal atmosphere of (760 mm. Hg).

In table 7 are given the determinations made on board, during the return from Tortugas to New York, together with the latitude and longitude of the stations.

In figure 3 the stations from Key West to New York are marked by crosses and the appended numbers indicate the number of cubic centi meters of per liter. The track of the steamer during the night is marked by a black line and the track during the day is unmarked. Since the steamer had a speed through the water of about 12 knots, actual diurnal variations could not be determined. If, however, we assume that the Gulf Stream arises from a source of uniform composi tion, those observations in the axis of the stream should show the diur nal variations, except for the modifications due to local meteorological differences. Although Trichospharium and other phytoplankton were present, and photosynthesis can occur at all depths less than 300 meters (light penetrating 1,000 meters), no marked or certain increase in in the sunshine was noted. At 5h20m a. m. August 2 there were 4.47 c.c. per liter and at 3 p. m. August 1 there was 4.50 c.c.; but no other pair of observations in the Gulf Stream shows a greater content in the afternoon than in the morning. Since oxygen is un doubtedly produced by these plants in the sunshine, the failure to observe an accumulation during the day probably lies in the fact that the temperature of the water rises about 1°, thus reducing the absorp tion coefficient for 02 by 0.08 c.c. per liter and causing a passage of 02 into the air. In contrast to this behavior of deep water, the 02 con centration of the shallow water of Tortugas varied from 3 to 4.5 at

about dawn to 4.5 to 7.0 at 3 p. m., the average maximum being shown in figure 4 opposite the station letters.

Discussion.

Determinations :of the pH from certain North Atlantic stations, table 8, made by Palitzsch (1912 b) compare favorably with those I have made in the Gulf Stream and in the deep water near Tortugas.

There is no increased amount of phytoplankton at Tortugas, but attached seaweed and symbiotic algae and diatoms at the bottom cause the great diurnal change in 02 concentration. On coral reefs the sym biotic algae of corals and actinians are very effective, and in lagoons or other water which is not too agitated the symbiotic algae of two species of the bottom medusa Cassiopea are a significant factor. One Cassiopea xamachana (11 cm. in diameter, weighing about 117 grams) in the sunlight gave out 1.9 c.c. 02 per hour, whereas in the dark it absorbed 2.8 c.c. per hour, showing that 4.7 c.c. per hour was produced by photosynthesis, at 30°. In other words, the given out in the day is about two-thirds the amount used at night.

The production of oxygen by plants by photosynthesis depends on a number of factors. The data found in the literature are all in terms of leaf surface and not volume or weight. Haberlandt found the capacity of the chloroplasts of different plants to be about the same—i. e., the rate of photosynthesis per unit area depended on the number of chloro plasts per unit area, as shown in table 9.

With the same plant, photosynthesis depends on temperature, light, and supply, and a lowering of any one of these factors may make it the limiting factor (law of minimum). Blackman showed that photo synthesis is about doubled by a rise of 10° in temperature. He showed this to be true of temperatures as high as 45°, provided the rate immedi ately after raising the temperature was calculated. With injurious temperatures the rate constantly falls, and the initial rate was estimated by extrapolation of the time curve.

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