2998 | ANNUAL REPORT SMITHSONIAN INSTITUTION, 1946 
sand, cinders, gravel, or crushed rock. On Ascension volcanic ash or 
pumice was used. 
The nutrient solutions of our land or shore installations are made 
up of salts of the principal plant foods, calcium, magnesium, phos- 
phorus, sulfur, and nitrogen, with the addition of indispensable “mi- 
chronutrient supplements,” chiefly iron, copper, manganese, molyb- 
denum, and zinc. With one notable exception, the composition of this 
nutrient solution is quite similar to that of sea water. That excep- 
tion is sodium chloride, which forms approximately 78 percent of 
the total dissolved solids in sea water. To marine plants in the usual 
concentrations this salt is harmless, to land and fresh-water plants it 
is quickly lethal. There is no problem regarding micronutrient sup- 
plements in sea water, for all the supplements that are ever supplied 
land plants, along with many more, including at least traces of a 
majority of the known elements, are present in sea water. 
In the seven seas we have the world’s greatest hydroponics set-up, 
with a limitless supply of nutrient solution immediately at hand. In 
the oceans, as in the hydroponics tanks, no plant growth is possible 
without the energy given up by the sun. Besides the nutrient mate- 
rials in solution, plants must have unlimited supplies of carbon di- 
oxide and water for their photosynthetic processes. The land plants 
derive their carbon dioxide from the atmosphere, their water from the 
nutrient solution. In the sea carbon dioxide, either as the dissolved 
gas or in the form of readily hydrolyzed bicarbonates, is so abundant 
as never to be a limiting factor to plant growth. When the nutrient 
solutions in the hydroponics tanks become exhausted the needed 
chemicals are added or fresh solutions made up and circulated through 
the tanks. In the sea comparable enrichment is brought about by the 
leaching and erosion of the constituents from the land,? as well as by 
the end products of the bacterial decomposition of past generations 
of marine plants and animals and the breaking down of complex 
inorganic substances. 
All the plant foods thus released, replenishing the nutrient sea- 
water solution, are redistributed and circulated by currents powered 
in large measure by the heat of the sun and in part by the earth’s 
rotation, which likewise is dependent upon the sun’s attraction. The 
earth’s rotation also brings about pronounced upwellings along the 
west coasts of continents, notably the west coast of the Americas and 
West Africa. These upwellings, along with convection currents, due 
to differences in temperature and salinity of various bodies of water, 
bring up other still untouched reserves of plant foods and dissolved 
gases for the use of the plants in the photic zone. Thus the nutrient 
2 Coker ventures the estimate that 8 billion metric tons of material from the land is 
annually being dumped into the sea. 
