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THE AMEBIC AN NATURALIST [Vol. XLVII 



of the sea, on account of its very limited range, except the veg- 

 etable plankton (and bacteria), is in marked contrast with that 

 on land. And if it were not for the broadcast scattering of plant 

 remains "the greater part of the bottom of the sea would be 

 bare, not only of vegetation, but also of the animal life dependent 

 on the vegetation." The source or sources of bottom deposits 

 was now investigated in detail. In this connection the origin of 

 the bottom deposits in Danish lakes is instructive. Wesenberg- 

 Lund has found a considerable amount of organic materials on 

 the bottom of these lakes. This layer is eaten by animals and a 

 bottom soil is formed which has passed through the digestive 

 systems of animals. This material is called gytje and is "formed 

 in pure clean water chiefly by the excremental agency of the bot- 

 tom-fauna. ' ' These organic materials are derived from the land, 

 the littoral zone, or from the plankton. In deep lakes the plank- 

 ton materials are dissolved before they reach the bottom, but in 

 shallow lakes the soft parts of the plankton are also added to this 

 layer. This condition naturally calls to the reviewer's mind the 

 activity of earthworms in the soil, and Dall's 2 discussion of the 

 banks of excrement formed by fish on the borders of the con- 

 tinental slopes. 



Returning now to the bottom deposits in Danish waters, it is 

 interesting to note the character of the organic bottom layer. 

 This forms a brown layer from 1-2 mm. thick, composed of 

 fluffy fine materials, both organic and inorganic. When tested 

 for cellulose but little was found, but large amounts of pectose 

 were present and similar relations resulted in tests of Zos- 

 tera, thus supporting the view that Zostera was an impor- 

 tant source of this organic material. Below this upper layer 

 is a dark blue one, and both layers are free from odor. 

 This kind of bottom is found in depths of more than 6 me- 

 ters. "When these bottom samples are examined it is found that 

 the amount of carbon is greater when Zostera is abundant, 

 rather than when plankton is abundant, and therefore Jensen 

 concludes that the "main source of organic matter in the sea 

 bottom must be due to the Zostera belt and not to the plankton 

 organisms." Bottom samples taken out at sea show that there is 

 a progressive diminution of carbon with distance from the shore, 

 and therefore he again concludes that: "the organic matter in 

 the sea bottom is mainly derived from the benthos formation at 

 s Pro. Biol. Soc. Wash., Vol. 5, pp. 10-11, 1890. 



