58 U. S. BUREAU OF FISHERIES 



about neutral or slightly acid (pH 7.1 to 6.5), while the lower water 

 was distinctly acid (pH 5.4 to 5.2), In those lakes containing larger 

 amounts of calcium and magnesium in solution the surface water 

 was alkaline (pH 8 to 8.9), but the lower water was usually on the 

 acid side (pH 6.8 to 6.5). In the hard-water lakes of southeastern 

 Wisconsin the upper stratum in summer ranges from pH 8.5 to 9.0. 

 while the lower water ranges from pH 7.6 to 7.2 even when it con- 

 tains considerable free carbon dioxide. 



In the soft-water lakes the centrifuge plankton yielded from 750 

 to 1,280 milligrams of dry organic matter per cubic meter of water. 

 In the lakes having somewhat harder water the range was from 970 

 to 3,850 milligrams of organic matter per cubic meter. Three lakes 

 having depths of 4 to 9 meters yielded more than 3,000 milligrams 

 per cubic meter, while two others with depths of 8 and 12 meters 

 yielded more than 2,000 milligrams. The yield of lakes more than 

 12 meters deep varied from about 1,000 to 1,800 milligrams. 



Computations per unit area on the basis of maximum depth give 

 very different results. The highest yield, namely, 3,850 milligrams 

 per cubic meter, was obtained in a lake with .a maximum depth of 4.5 

 meters, which represents 17.3 grams per square meter of surface. A 

 yield of 3,238 milligrams per cubic meter was obtained in a lake 

 having a maximum depth of 9 meters, and this represents a yield of 

 29.1 grams per square meter of surface. On the other hand, the 

 deepest lake yielded only 1,080 milligrams of dry organic matter per 

 cubic meter, which represents 37.8 grams per square meter of surface 

 for a maximum depth of 35 meters. 



The centrifuge plankton of six hard-water lakes of southeastern 

 "Wisconsin, obtained in September and October, yielded from 876 to 

 1,875 milligrams of dry organic matter per cubic meter of water. 

 These results are of the same general order of magnitude as those of 

 the northern lakes having a medium amount of fixed carbon dioxide 

 in solution, with the exception of the shallower northern lakes. No 

 observations were made on southern lakes having a maximum depth 

 of 4 to 8 meters. 



These investigations have been carried on by Dr. Chancey Juday, 

 of the Department of Zoology, University of Wisconsin. 



FOULING or ships' BOTTOMS 



The investigation on the fouling of ships' bottoms was continued 

 during the past year by Dr. J. P. Visscher at New York City, Nor- 

 folk, Va., and Beaufort, N. C. About 10 ships per month were exam- 

 ined, giving an approximate total of 225 ships examined during the 

 course of the investigation. Data concerning the length of voyage, 

 route, ports visited, etc., were obtained in addition to the collection 

 of the fouling material on the hulls. These data, gathered from more 

 than 200 ships, have been tabulated and show that the organisms 

 occuring most frequently on the bottom of marine vessels are algse, 

 hydroids, and barnacles. The following table gives the results of 

 the examinations of the first 157 ships, 141 of which, or 89 per cent, 

 were foul : 



