90 SECRETS OF ANIMAL LIFE 



distinctive population of their own. From the 

 shore to a depth of two or three fathoms are the 

 meadows of the sea-grass, with true roots and 

 flowers and very long ribbon-like leaves, familiar as 

 a packing and stuffing material and as a covering for 

 Italian flasks of , wine or oil. Mixed with this Zostera 

 are the seaweeds proper, attached but without 

 true roots, enlivening the grass-green with beautiful 

 reds, browns, and olives. Farther out the sea- 

 weed vegetation thins, until it disappears at a 

 depth of about twenty-five fathoms. It is a crowded 

 vegetative area, able to support a crowded animal 

 life; the waving sea-grass is often as thick as the 

 stems in a cornfield, and Professor Petersen notes 

 that the total annual yield in Danish waters is over 

 8000 million kilograms of dry matter, about four 

 times the quantity of hay produced in a year in 

 Denmark. This suggests further utilization the 

 Zostera is already used for fodder, for paper-mak- 

 ing, for making explosives, and in other ways but 

 sea-grass is a difficult harvest to reap, and perhaps 

 its greatest value is the indirect one, that it forms a 

 basal food supply for animals on which many food 

 fishes mostly depend. For what Professor Petersen 

 and his colleagues have discovered is that the surface 

 of the mud (or clay farther from shore) is covered 

 by a thin layer of detritus of very nutritive quality, 

 and that this is mainly produced by fragments of 

 sea-grass and littoral seaweeds, the downward sink- 

 ing Plankton counting for little. Examination of 

 the stomach contents of common non-predatory 



