ECONOMIC IMPORTANCE OF DIATOMS — MANN. 385 



of the inorganic substances of the earth into organic materials that 

 shall serve as food. The elements necessary to sustain life must be 

 brought into certain chemical relationships, known as a class as or- 

 ganic substances, before the animal can draw upon these to supply its 

 life processes. In other w^ords, carbon, oxygen, hydrogen, nitrogen, 

 phosphorus, potash, etc., will not juggle themselves into edible com- 

 pounds. It is only by the alchemy of the green, chlorophyl-bearing 

 plants that these combinations are brought about. The diatom is 

 the smallest of all the green, chlorophyl-bearing plants; but despite 

 its insignificant size, these lilliputian workers are so numerous that 

 the sum total of their activity is almost beyond calculation. Prof. 

 Kofoid has estimated that the average number of diatoms in 1 cubic 

 meter of water in the Illinois River is 35,558,462. Thriving abund- 

 antly in all the w^aters of the earth, fresh and salt, from the north 

 pole to the south, the countless myriads of these plants are turning 

 the substances held in solution in the waters of the streams, lakes, 

 and seas into living material and are doing this in that strange 

 alembic where it always takes place, namely, the green, chloroj^hyl- 

 grain. By harnessing in some way a sunbeam to its machinery it 

 turns out from the crude material of mineral matter the vital mate- 

 rial of plant tissue, and on this plant tissue there feeds directly or 

 indirectly most of the animal life of the sea. Some of the minuter 

 forms of economic value to mankind, like the smaller fishes (for 

 example, the sardine) and the shellfish (clams and oysters) make 

 these plants their principal if not their exclusive food. The teem- 

 ing swarms of tiny animal creatures, of which the copepods may be 

 cited as as an example, are the links between the diatoms and those 

 other organisms which in turn prey upon them. 



And thus, as upon the land the carnivore feeds upon the herbivore 

 and the herbivore feeds upon the plant, so in the sea its animal 

 denizens may be referred back in their food supply to the final 

 source, the diatoms. It may therefore be said, without stretching 

 the truth, that these plants are the grass of the sea, because they 

 occupy the same important relationship toward the life of the 

 sea that grass does toward the life of the land. It is not meant 

 by this that other marine plants do not contribute to the store of 

 animal food. Many of the brown and red seaweeds form the pas- 

 tures of animal sea life; and one plant especially, the so-called eel 

 grass, Zostera Tnarina, is of great importance to those forms of life 

 inhabiting the shallower waters along the shore and especially of 

 the bays and estuaries indenting the coast. Although Zostera does 

 not appear to be extensively preyed upon while it is growing, it 

 becomes a highly nutritious feast for myriads of forms of animal 

 life at the time of its decay. But its usefulness in this respect is 

 greatly circumscribed because it is not available during the greater 



