596 ANNUAL KEPORT SMITHSONIAN INSTITUTION, 1917. 



the earth when it was much hotter than it is now, the sea has been 

 accumulating a wealth of materials, the most conspicuous of w^hich 

 is the salt which makes it briny. These liave been leached out of the 

 rocks and soils and, in a way, the sea may be said to be a solution (ff 

 the land. It even contains traces of such inert substances as the 

 precious metals like gold, but its really precious store consists of the 

 same minerals which make our productive soils, or which the farmer 

 supplies to his land when he fertilizes it. In fact, some of the very 

 fertilizer for which the farmer pays, and wliich through carelessness 

 or misfortune is washed from his fields into the watercourses, un- 

 doubtedly finds its Avay in course of time to add to the sea's store. It 

 is not entirely lost to man, for with other materials of its kind it 

 becomes converted into marine vegetation, just as some of it would 

 have entered into farm crops if it had been left in the fields. It 

 produces not only the " sea weeds " of the grosser kind, with which 

 every visitor to the seashore is more or less familiar, but a wealth of 

 microscopic plants, individually too small for human vision, but of 

 an aggregate volume surpassing comprehension, some of them float- 

 ing freely in the water and others forming carpets on the bottom in 

 the shallows or patches on every fixed or floating body. This vege- 

 tation, in general, is more luxuriant in proximity to the coast than 

 in the waters far removed from land, and this is true not only of 

 the bottom dwelling forms, which can not live in the lightless regions 

 of the gi'eat depths, but of the floating species which dwell at or 

 near the surface. The abounding plant life near the shores, and 

 particularly in salt and brackish estuaries and lagoons, is probably 

 in no small degree correlated with the never-ceasing flow of fertilizer 

 materials, the wash of the soil, which the rivers bring down to the 

 coasts. 



It is this vegetation, but particularly the microscopic kinds, both 

 bottom dwelling and floating, which forms the great pastures of the 

 deep on which the animal life of the sea is as rigidly dependent as 

 are the land animals on the produce of the soil, and of which man 

 indirectly avails himself when he partakes of sea food. 



There are many interesting adaptations of structure and habit 

 which complete the cycle from the soil through the sea and back 

 again to the land, but one instance will suffice as a type. The wash 

 from a carelessly tilled farm, or the waste of a household, finds its 

 way into a river on the Atlantic coast and is carried in a state of solu- 

 tion to one of the estuaries or bays which indent the shore line. 

 There it is absorbed as nourishment by one of a group of microscopic 

 plants known as diatoms, which use the same sort of food and elabo- 

 rate it in the same way as land plants, but obtain it from the dis- 

 solved materials of the water in which they are bathed, instead of 

 seeking it through the medium of roots thrust into the soil and leaves 



