SUN AND HARVEST OF THE SEA—SCHMITT 299 
solution is renewed and kept in constant circulation and is also 
aerated. Important adjuncts to the mixing apparatus of the oceans 
are the drifts and tides, the waves and breakers, and the winds and 
storms. 
THE MBADOWS OF THE SEA* 
The plants which form the greater bulk of plant life in the sea 
are microscopic, swimming or floating freely but more or less pas- 
sively at or relatively near the surface. That this planktonic plant 
life is so very tiny is Nature’s way of meeting the problem of deriving 
nutriment from a very dilute solution. The salt content of water is 
generally expressed in parts per thousand, per mille, instead of per- 
cent. It is a well-known physical fact that the smaller the body, the 
greater the ratio of surface to volume. The greater the surface for a 
given body, the greater its power of absorption of the nutriment from 
solution as well as energy from the sun. Best known of these plant 
forms are the diatoms and the dinoflagellates or peridinians. They 
have been most intensively studied not only because they are so 
numerous, but also because they can be so conveniently screened from 
the sea with the fine-meshed silken tow nets generally used for 
sampling plankton. 
Less well known because of their very much smaller size are other 
plant forms which readily pass through the meshes of the tow nets, 
even though the meshes run as small as sixty-four hundredths of a 
millimeter. We speak here of the coccolithophorids, the yellow 
algae, as distinguished from the yellow-green diatoms, which under 
ordinary circumstances seem only to be caught by accident in our 
silk nets. They are obtained for study by centrifuging sea water, or 
by running it through filter paper. By some investigators the role 
played by the coccolithophorids in the economy of the seas is con- 
sidered at least as important as their larger relatives, the diatoms and 
peridinians, along with a widely distributed true green algalike 
plant, Halosphera viridis. In the Antarctic region this plant is one 
of the dominant forms of planktonic plant life, standing next in 
importance to the diatoms. 
As the plants in the hydroponics tank need support of some kind, so 
also must the marine plants be supported in their nutrient medium if 
they are to remain within the so-called photic zone. This zone com- 
prises that part of the upper levels of the sea to which the sun’s light 
and radiant energy penetrates in suflicient strength to permit photosyn- 
3 Not mentioned are the algae of the littoral zone, including the giant kelps and free- 
floating sargassum, and the higher forms of marine plants such as the eel grass of 
northern waters and the turtle grass of southern waters. All play important roles in the 
economy of the sea. The story of their several roles is as interesting as the one involving 
the planktonic forms of plant life. 
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